Oracle/PLSQL Topics
Oracle is a relational database technology.
PLSQL stands for "Procedural Language extensions to SQL", and can be used in Oracle databases. PLSQL is closely integrated into the SQL language, yet it adds programming constructs that are not native to SQL.
We've categorized Oracle and PLSQL into the following topics:
SQL: SELECT Statement
The SELECT statement allows you to retrieve records from one or more tables in your database.
The syntax for the SELECT statement is:
SELECT columns
FROM tables
WHERE predicates;
Example #1
Let's take a look at how to select all fields from a table.
SELECT *
FROM supplier
WHERE city = 'Newark';
In our example, we've used * to signify that we wish to view all fields from the supplier table where the supplier resides in Newark.
Example #2
You can also choose to select individual fields as opposed to all fields in the table.
For example:
SELECT name, city, state
FROM supplier
WHERE supplier_id > 1000;
This select statement would return all name, city, and state values from the supplier table where the supplier_id value is greater than 1000.
Example #3
You can also use the select statement to retrieve fields from multiple tables.
SELECT orders.order_id, supplier.name
FROM supplier, orders
WHERE supplier.supplier_id = orders.supplier_id;
The result set would display the order_id and suppier name fields where the supplier_id value existed in both the supplier and orders table.
SQL: DISTINCT Clause
The DISTINCT clause allows you to remove duplicates from the result set. The DISTINCT clause can only be used with select statements.
The syntax for the DISTINCT clause is:
SELECT DISTINCT columns
FROM tables
WHERE predicates;
Example #1
Let's take a look at a very simple example.
SELECT DISTINCT city
FROM supplier;
This SQL statement would return all unique cities from the supplier table.
Example #2
The DISTINCT clause can be used with more than one field.
For example:
SELECT DISTINCT city, state
FROM supplier;
This select statement would return each unique city and state combination. In this case, the distinct applies to each field listed after the DISTINCT keyword.
SQL: COUNT Function
The COUNT function returns the number of rows in a query.
The syntax for the COUNT function is:
SELECT COUNT(expression)
FROM tables
WHERE predicates;
Note:
The COUNT function will only count those records in which the field in the brackets is NOT NULL.
For example, if you have the following table called Suppliers:
| Supplier_ID | Supplier_Name | State |
| 1 | IBM | CA |
| 2 | Microsoft | |
| 3 | NVidia | |
The result for this query will return 3.
Select COUNT(Supplier_ID) From Suppliers;
While the result for the next query will only return 1, since there is only one row in the Suppliers table where the State field is NOT NULL.
Select COUNT(State) From Suppliers;
Simple Example
For example, you might wish to know how many employees have a salary that is above $25,000 / year.
SELECT COUNT(*) as "Number of employees"
FROM employees
WHERE salary > 25000;
In this example, we've aliased the count(*) field as "Number of employees". As a result, "Number of employees" will display as the field name when the result set is returned.
Example using DISTINCT
You can use the DISTINCT clause within the COUNT function.
For example, the SQL statement below returns the number of unique departments where at least one employee makes over $25,000 / year.
SELECT COUNT(DISTINCT department) as "Unique departments"
FROM employees
WHERE salary > 25000;
Again, the count(DISTINCT department) field is aliased as "Unique departments". This is the field name that will display in the result set.
Example using GROUP BY
In some cases, you will be required to use a GROUP BY clause with the COUNT function.
For example, you could use the COUNT function to return the name of the department and the number of employees (in the associated department) that make over $25,000 / year.
SELECT department, COUNT(*) as "Number of employees"
FROM employees
WHERE salary > 25000
GROUP BY department;
Because you have listed one column in your SELECT statement that is not encapsulated in the COUNT function, you must use a GROUP BY clause. The department field must, therefore, be listed in the GROUP BY section.
TIP: Performance Tuning
Since the COUNT function will return the same results regardless of what NOT NULL field(s) you include as the COUNT function parameters (ie: within the brackets), you can change the syntax of the COUNT function to COUNT(1) to get better performance as the database engine will not have to fetch back the data fields.
For example, based on the example above, the following syntax would result in better performance:
SELECT department, COUNT(1) as "Number of employees"
FROM employees
WHERE salary > 25000
GROUP BY department;
Now, the COUNT function does not need to retrieve all fields from the employees table as it had to when you used the COUNT(*) syntax. It will merely retrieve the numeric value of 1 for each record that meets your criteria.
SQL: SUM Function
The SUM function returns the summed value of an expression.
The syntax for the SUM function is:
SELECT SUM(expression )
FROM tables
WHERE predicates;
expression can be a numeric field or formula.
Simple Example
For example, you might wish to know how the combined total salary of all employees whose salary is above $25,000 / year.
SELECT SUM(salary) as "Total Salary"
FROM employees
WHERE salary > 25000;
In this example, we've aliased the sum(salary) field as "Total Salary". As a result, "Total Salary" will display as the field name when the result set is returned.
Example using DISTINCT
You can use the DISTINCT clause within the SUM function. For example, the SQL statement below returns the combined total salary of unique salary values where the salary is above $25,000 / year.
SELECT SUM(DISTINCT salary) as "Total Salary"
FROM employees
WHERE salary > 25000;
If there were two salaries of $30,000/year, only one of these values would be used in the SUM function.
Example using a Formula
The expression contained within the SUM function does not need to be a single field. You could also use a formula. For example, you might want the net income for a business. Net Income is calculated as total income less total expenses.
SELECT SUM(income - expenses) as "Net Income"
FROM gl_transactions;
You might also want to perform a mathematical operation within a SUM function. For example, you might determine total commission as 10% of total sales.
SELECT SUM(sales * 0.10) as "Commission"
FROM order_details;
Example using GROUP BY
In some cases, you will be required to use a GROUP BY clause with the SUM function.
For example, you could also use the SUM function to return the name of the department and the total sales (in the associated department).
SELECT department, SUM(sales) as "Total sales"
FROM order_details
GROUP BY department;
Because you have listed one column in your SELECT statement that is not encapsulated in the SUM function, you must use a GROUP BY clause. The department field must, therefore, be listed in the GROUP BY section.
SQL: MIN Function
The MIN function returns the minimum value of an expression.
The syntax for the MIN function is:
SELECT MIN(expression )
FROM tables
WHERE predicates;
Simple Example
For example, you might wish to know the minimum salary of all employees.
SELECT MIN(salary) as "Lowest salary"
FROM employees;
In this example, we've aliased the min(salary) field as "Lowest salary". As a result, "Lowest salary" will display as the field name when the result set is returned.
Example using GROUP BY
In some cases, you will be required to use a GROUP BY clause with the MIN function.
For example, you could also use the MIN function to return the name of each department and the minimum salary in the department.
SELECT department, MIN(salary) as "Lowest salary"
FROM employees
GROUP BY department;
Because you have listed one column in your SELECT statement that is not encapsulated in the MIN function, you must use a GROUP BY clause. The department field must, therefore, be listed in the GROUP BY section.
SQL: MAX Function
The MAX function returns the maximum value of an expression.
The syntax for the MAX function is:
SELECT MAX(expression )
FROM tables
WHERE predicates;
Simple Example
For example, you might wish to know the maximum salary of all employees.
SELECT MAX(salary) as "Highest salary"
FROM employees;
In this example, we've aliased the max(salary) field as "Highest salary". As a result, "Highest salary" will display as the field name when the result set is returned.
Example using GROUP BY
In some cases, you will be required to use a GROUP BY clause with the MAX function.
For example, you could also use the MAX function to return the name of each department and the maximum salary in the department.
SELECT department, MAX(salary) as "Highest salary"
FROM employees
GROUP BY department;
Because you have listed one column in your SELECT statement that is not encapsulated in the MAX function, you must use a GROUP BY clause. The department field must, therefore, be listed in the GROUP BY section.
Frequently Asked Questions
Question: I'm trying to pull some info out of a table. To simplify, let's say the table (report_history) has 4 columns:
user_name, report_job_id, report_name, report_run_date.
Each time a report is run in Oracle, a record is written to this table noting the above info. What I am trying to do is pull from this table when the last time each distinct report was run and who ran it last.
My initial query:
SELECT report_name, max(report_run_date)
FROM report_history
GROUP BY report_name
runs fine. However, it does not provide the name of the user who ran the report.
Adding user_name to both the select list and to the group by clause returns multiple lines for each report; the results show the last time each person ran each report in question. (i.e. User1 ran Report 1 on 01-JUL-03, User2 ran Report1 on 01-AUG-03). I don't want that....I just want to know who ran a particular report the last time it was run.
Any suggestions?
Answer: This is where things get a bit complicated. The SQL statement below will return the results that you want:
SELECT rh.user_name, rh.report_name, rh.report_run_date
FROM report_history rh,
(SELECT max(report_run_date) as maxdate, report_name
FROM report_history
GROUP BY report_name) maxresults
WHERE rh.report_name = maxresults.report_name
AND rh.report_run_date= maxresults.maxdate;
Let's take a few moments to explain what we've done.
First, we've aliased the first instance of the report_history table as rh.
Second, we've included two components in our FROM clause. The first is the table called report_history (aliased as rh). The second is a select statement:
(SELECT max(report_run_date) as maxdate, report_name
FROM report_history
GROUP BY report_name) maxresults
We've aliased the max(report_run_date) as maxdate and we've aliased the entire result set as maxresults.
Now, that we've created this select statement within our FROM clause, Oracle will let us join these results against our original report_history table. So we've joined the report_name and report_run_date fields between the tables called rh and maxresults. This allows us to retrieve the report_name, max(report_run_date) as well as the user_name.
Question: I need help in an SQL query. I have a table in Oracle called orders which has the following fields: order_no, customer, and amount.
I need a query that will return the customer who has ordered the highest total amount.
Answer: The following SQL should return the customer with the highest total amount in the orders table.
select query1.* from
(SELECT customer, Sum(orders.amount) AS total_amt
FROM orders
GROUP BY orders.customer) query1,
(select max(query2.total_amt) as highest_amt
from (SELECT customer, Sum(orders.amount) AS total_amt
FROM orders
GROUP BY orders.customer) query2) query3
where query1.total_amt = query3.highest_amt;
This SQL statement will summarize the total orders for each customer and then return the customer with the highest total orders. This syntax is optimized for Oracle and may not work for other database technologies.
Question: I'm trying to retrieve some info from an Oracle database. I've got a table named Scoring with two fields - Name and Score. What I want to get is the highest score from the table and the name of the player.
Answer: The following SQL should work:
SELECT Name, Score
FROM Scoring
WHERE Score = (select Max(Score) from Scoring);
SQL: WHERE Clause
The WHERE clause allows you to filter the results from an SQL statement - select, insert, update, or delete statement.
It is difficult to explain the basic syntax for the WHERE clause, so instead, we'll take a look at some examples.
Example #1
SELECT *
FROM supplier
WHERE supplier_name = 'IBM';
In this first example, we've used the WHERE clause to filter our results from the supplier table. The SQL statement above would return all rows from the supplier table where the supplier_name is IBM. Because the * is used in the select, all fields from the supplier table would appear in the result set.
Example #2
SELECT supplier_id
FROM supplier
WHERE supplier_name = 'IBM'
or supplier_city = 'Newark';
We can define a WHERE clause with multiple conditions. This SQL statement would return all supplier_id values where the supplier_name is IBM or the supplier_city is Newark.
Example #3
SELECT supplier.suppler_name, orders.order_id
FROM supplier, orders
WHERE supplier.supplier_id = orders.supplier_id
and supplier.supplier_city = 'Atlantic City';
We can also use the WHERE clause to join multiple tables together in a single SQL statement. This SQL statement would return all supplier names and order_ids where there is a matching record in the supplier and orders tables based on supplier_id, and where the supplier_city is Atlantic City.
SQL: "AND" Condition
The AND condition allows you to create an SQL statement based on 2 or more conditions being met. It can be used in any valid SQL statement - select, insert, update, or delete.
The syntax for the AND condition is:
SELECT columns
FROM tables
WHERE column1 = 'value1'
and column2 = 'value2';
The AND condition requires that each condition be must be met for the record to be included in the result set. In this case, column1 has to equal 'value1' and column2 has to equal 'value2'.
Example #1
The first example that we'll take a look at involves a very simple example using the AND condition.
SELECT *
FROM supplier
WHERE city = 'New York'
and type = 'PC Manufacturer';
This would return all suppliers that reside in New York and are PC Manufacturers. Because the * is used in the select, all fields from the supplier table would appear in the result set.
Example #2
Our next example demonstrates how the AND condition can be used to "join" multiple tables in an SQL statement.
SELECT order.order_id, supplier.supplier_name
FROM supplier, order
WHERE supplier.supplier_id = order.supplier_id
and supplier.supplier_name = 'IBM';
This would return all rows where the supplier_name is IBM. And the supplier and order tables are joined on supplier_id. You will notice that all of the fields are prefixed with the table names (ie: order.order_id). This is required to eliminate any ambiguity as to which field is being referenced; as the same field name can exist in both the supplier and order tables.
In this case, the result set would only display the order_id and supplier_name fields (as listed in the first part of the select statement.).
SQL: "OR" Condition
The OR condition allows you to create an SQL statement where records are returned when any one of the conditions are met. It can be used in any valid SQL statement - select, insert, update, or delete.
The syntax for the OR condition is:
SELECT columns
FROM tables
WHERE column1 = 'value1'
or column2 = 'value2';
The OR condition requires that any of the conditions be must be met for the record to be included in the result set. In this case, column1 has to equal 'value1' OR column2 has to equal 'value2'.
Example #1
The first example that we'll take a look at involves a very simple example using the OR condition.
SELECT *
FROM supplier
WHERE city = 'New York'
or city = 'Newark';
This would return all suppliers that reside in either New York or Newark. Because the * is used in the select, all fields from the supplier table would appear in the result set.
Example #2
The next example takes a look at three conditions. If any of these conditions is met, the record will be included in the result set.
For example:
SELECT supplier_id
FROM supplier
WHERE name = 'IBM'
or name = 'Hewlett Packard'
or name = 'Gateway';
This SQL statement would return all supplier_id values where the supplier's name is either IBM, Hewlett Packard or Gateway.
SQL: Combining the "AND" and "OR" Conditions
The AND and OR conditions can be combined in a single SQL statement. It can be used in any valid SQL statement - select, insert, update, or delete.
When combining these conditions, it is important to use brackets so that the database knows what order to evaluate each condition.
Example #1
The first example that we'll take a look at an example that combines the AND and OR conditions.
SELECT *
FROM supplier
WHERE (city = 'New York' and name = 'IBM')
or (city = 'Newark');
This would return all suppliers that reside in either New York whose name is IBM, all supplies that reside in Newark. The brackets determine what order the AND and OR conditions are evaluated in.
Example #2
The next example takes a look at a more complex statement.
For example:
SELECT supplier_id
FROM supplier
WHERE (name = 'IBM')
or (name = 'Hewlett Packard' and city = 'Atlantic City')
or (name = 'Gateway' and status = 'Active' and city = 'Burma');
This SQL statement would return all supplier_id values where the supplier's name is IBM or the name is Hewlett Packard and the city is Atlantic City or the name is Gateway and the city is Burma.
SQL: LIKE Condition
The LIKE condition allows you to use wildcards in the where clause of an SQL statement. This allows you to perform pattern matching. The LIKE condition can be used in any valid SQL statement - select, insert, update, or delete.
The patterns that you can choose from are:
% allows you to match any string of any length (including zero length)
_ allows you to match on a single character
Examples using % wildcard
The first example that we'll take a look at involves using % in the where clause of a select statement. We are going to try to find all of the suppliers whose name begins with 'Hew'.
SELECT * FROM supplier
WHERE supplier_name like 'Hew%';
You can also using the wildcard multiple times within the same string. For example,
SELECT * FROM supplier
WHERE supplier_name like '%bob%';
In this example, we are looking for all suppliers whose name contains the characters 'bob'.
You could also use the LIKE condition to find suppliers whose name does not start with 'T'. For example,
SELECT * FROM supplier
WHERE supplier_name not like 'T%';
By placing the not keyword in front of the LIKE condition, you are able to retrieve all suppliers whose name does not start with 'T'.
Examples using _ wildcard
Next, let's explain how the _ wildcard works. Remember that the _ is looking for only one character.
For example,
SELECT * FROM supplier
WHERE supplier_name like 'Sm_th';
This SQL statement would return all suppliers whose name is 5 characters long, where the first two characters is 'Sm' and the last two characters is 'th'. For example, it could return suppliers whose name is 'Smith', 'Smyth', 'Smath', 'Smeth', etc.
Here is another example,
SELECT * FROM supplier
WHERE account_number like '12317_';
You might find that you are looking for an account number, but you only have 5 of the 6 digits. The example above, would retrieve potentially 10 records back (where the missing value could equal anything from 0 to 9). For example, it could return suppliers whose account numbers are:
123170
123171
123172
123173
123174
123175
123176
123177
123178
123179.
Examples using Escape Characters
Next, in Oracle, let's say you wanted to search for a % or a _ character in a LIKE condition. You can do this using an Escape character.
Please note that you can define an escape character as a single character (length of 1) ONLY.
For example,
SELECT * FROM supplier
WHERE supplier_name LIKE '!%' escape '!';
This SQL statement identifies the ! character as an escape character. This statement will return all suppliers whose name is %.
Here is another more complicated example:
SELECT * FROM supplier
WHERE supplier_name LIKE 'H%!%' escape '!';
This example returns all suppliers whose name starts with H and ends in %. For example, it would return a value such as 'Hello%'.
You can also use the Escape character with the _ character. For example,
SELECT * FROM supplier
WHERE supplier_name LIKE 'H%!_' escape '!';
This example returns all suppliers whose name starts with H and ends in _. For example, it would return a value such as 'Hello_'.
SQL: "IN" Function
The IN function helps reduce the need to use multiple OR conditions.
The syntax for the IN function is:
SELECT columns
FROM tables
WHERE column1 in (value1, value2, .... value_n);
This SQL statement will return the records where column1 is value1, value2..., or value_n. The IN function can be used in any valid SQL statement - select, insert, update, or delete.
Example #1
The following is an SQL statement that uses the IN function:
SELECT *
FROM supplier
WHERE supplier_name in ( 'IBM', 'Hewlett Packard', 'Microsoft');
This would return all rows where the supplier_name is either IBM, Hewlett Packard, or Microsoft. Because the * is used in the select, all fields from the supplier table would appear in the result set.
It is equivalent to the following statement:
SELECT *
FROM supplier
WHERE supplier_name = 'IBM'
OR supplier_name = 'Hewlett Packard'
OR supplier_name = 'Microsoft';
As you can see, using the IN function makes the statement easier to read and more efficient.
Example #2
You can also use the IN function with numeric values.
SELECT *
FROM orders
WHERE order_id in (10000, 10001, 10003, 10005);
This SQL statement would return all orders where the order_id is either 10000, 10001, 10003, or 10005.
It is equivalent to the following statement:
SELECT *
FROM orders
WHERE order_id = 10000
OR order_id = 10001
OR order_id = 10003
OR order_id = 10005;
Example #3 - "NOT IN"
The IN function can also be combined with the NOT operator.
For example,
SELECT *
FROM supplier
WHERE supplier_name not in ( 'IBM', 'Hewlett Packard', 'Microsoft');
This would return all rows where the supplier_name is neither IBM, Hewlett Packard, or Microsoft. Sometimes, it is more efficient to list the values that you do not want, as opposed to the values that you do want.
SQL: BETWEEN Condition
The BETWEEN condition allows you to retrieve values within a range.
The syntax for the BETWEEN condition is:
SELECT columns
FROM tables
WHERE column1 between value1 and value2;
This SQL statement will return the records where column1 is within the range of value1 and value2 (inclusive). The BETWEEN function can be used in any valid SQL statement - select, insert, update, or delete.
Example #1 - Numbers
The following is an SQL statement that uses the BETWEEN function:
SELECT *
FROM suppliers
WHERE supplier_id between 5000 AND 5010;
This would return all rows where the supplier_id is between 5000 and 5010, inclusive. It is equivalent to the following SQL statement:
SELECT *
FROM suppliers
WHERE supplier_id >= 5000
AND supplier_id <= 5010;
Example #2 - Dates
You can also use the BETWEEN function with dates.
SELECT *
FROM orders
WHERE order_date between to_date ('2003/01/01', 'yyyy/mm/dd')
AND to_date ('2003/12/31', 'yyyy/mm/dd');
This SQL statement would return all orders where the order_date is between Jan 1, 2003 and Dec 31, 2003 (inclusive).
It would be equivalent to the following SQL statement:
SELECT *
FROM orders
WHERE order_date >= to_date('2003/01/01', 'yyyy/mm/dd')
AND order_date <= to_date('2003/12/31','yyyy/mm/dd');
Example #3 - NOT BETWEEN
The BETWEEN function can also be combined with the NOT operator.
For example,
SELECT *
FROM suppliers
WHERE supplier_id not between 5000 and 5500;
This would be equivalent to the following SQL:
SELECT *
FROM suppliers
WHERE supplier_id < 5000
OR supplier_id > 5500;
In this example, the result set would exclude all supplier_id values between the range of 5000 and 5500 (inclusive).
SQL: EXISTS Condition
The EXISTS condition is considered "to be met" if the subquery returns at least one row.
The syntax for the EXISTS condition is:
SELECT columns
FROM tables
WHERE EXISTS ( subquery );
The EXISTS condition can be used in any valid SQL statement - select, insert, update, or delete.
Example #1
Let's take a look at a simple example. The following is an SQL statement that uses the EXISTS condition:
SELECT *
FROM suppliers
WHERE EXISTS
(select *
from orders
where suppliers.supplier_id = orders.supplier_id);
This select statement will return all records from the suppliers table where there is at least one record in the orders table with the same supplier_id.
Example #2 - NOT EXISTS
The EXISTS condition can also be combined with the NOT operator.
For example,
SELECT *
FROM suppliers
WHERE not exists (select * from orders Where suppliers.supplier_id = orders.supplier_id);
This will return all records from the suppliers table where there are no records in the orders table for the given supplier_id.
Example #3 - DELETE Statement
The following is an example of a delete statement that utilizes the EXISTS condition:
DELETE FROM suppliers
WHERE EXISTS
(select *
from orders
where suppliers.supplier_id = orders.supplier_id);
| UPDATE supplier SET supplier_name = ( SELECT customer.name
FROM customers
WHERE customers.customer_id = supplier.supplier_id) WHERE EXISTS
( SELECT customer.name
FROM customers
WHERE customers.customer_id = supplier.supplier_id); |
Example #4 - UPDATE Statement
The following is an example of an update statement that utilizes the EXISTS condition:
Example #5 - INSERT Statement
The following is an example of an insert statement that utilizes the EXISTS condition:
INSERT INTO supplier
(supplier_id, supplier_name)
SELECT account_no, name
FROM suppliers
WHERE exists (select * from orders Where suppliers.supplier_id = orders.supplier_id);
SQL: GROUP BY Clause
The GROUP BY clause can be used in a SELECT statement to collect data across multiple records and group the results by one or more columns.
The syntax for the GROUP BY clause is:
SELECT column1, column2, ... column_n, aggregate_function (expression)
FROM tables
WHERE predicates
GROUP BY column1, column2, ... column_n;
aggregate_function can be a function such as SUM, COUNT, MIN, or MAX.
Example using the SUM function
For example, you could also use the SUM function to return the name of the department and the total sales (in the associated department).
SELECT department, SUM(sales) as "Total sales"
FROM order_details
GROUP BY department;
Because you have listed one column in your SELECT statement that is not encapsulated in the SUM function, you must use a GROUP BY clause. The department field must, therefore, be listed in the GROUP BY section.
Example using the COUNT function
For example, you could use the COUNT function to return the name of the department and the number of employees (in the associated department) that make over $25,000 / year.
SELECT department, COUNT(*) as "Number of employees"
FROM employees
WHERE salary > 25000
GROUP BY department;
Example using the MIN function
For example, you could also use the MIN function to return the name of each department and the minimum salary in the department.
SELECT department, MIN(salary) as "Lowest salary"
FROM employees
GROUP BY department;
Example using the MAX function
For example, you could also use the MAX function to return the name of each department and the maximum salary in the department.
SELECT department, MAX(salary) as "Highest salary"
FROM employees
GROUP BY department;
SQL: HAVING Clause
The HAVING clause is used in combination with the GROUP BY clause. It can be used in a SELECT statement to filter the records that a GROUP BY returns.
The syntax for the HAVING clause is:
SELECT column1, column2, ... column_n, aggregate_function (expression)
FROM tables
WHERE predicates
GROUP BY column1, column2, ... column_n
HAVING condition1 ... condition_n;
aggregate_function can be a function such as SUM, COUNT, MIN, or MAX.
Example using the SUM function
For example, you could also use the SUM function to return the name of the department and the total sales (in the associated department). The HAVING clause will filter the results so that only departments with sales greater than $1000 will be returned.
SELECT department, SUM(sales) as "Total sales"
FROM order_details
GROUP BY department
HAVING SUM(sales) > 1000;
Example using the COUNT function
For example, you could use the COUNT function to return the name of the department and the number of employees (in the associated department) that make over $25,000 / year. The HAVING clause will filter the results so that only departments with at least 25 employees will be returned.
SELECT department, COUNT(*) as "Number of employees"
FROM employees
WHERE salary > 25000
GROUP BY department
HAVING COUNT(*) > 10;
Example using the MIN function
For example, you could also use the MIN function to return the name of each department and the minimum salary in the department. The HAVING clause will return only those departments where the starting salary is $35,000.
SELECT department, MIN(salary) as "Lowest salary"
FROM employees
GROUP BY department
HAVING MIN(salary) = 35000;
Example using the MAX function
For example, you could also use the MAX function to return the name of each department and the maximum salary in the department. The HAVING clause will return only those departments whose maximum salary is less than $50,000.
SELECT department, MAX(salary) as "Highest salary"
FROM employees
GROUP BY department
HAVING MAX(salary) <>
SQL: ORDER BY Clause
The ORDER BY clause allows you to sort the records in your result set. The ORDER BY clause can only be used in SELECT statements.
The syntax for the ORDER BY clause is:
SELECT columns
FROM tables
WHERE predicates
ORDER BY column ASC/DESC;
The ORDER BY clause sorts the result set based on the columns specified. If the ASC or DESC value is omitted, the system assumed ascending order.
ASC indicates ascending order. (default)
DESC indicates descending order.
Example #1
SELECT supplier_city
FROM supplier
WHERE supplier_name = 'IBM'
ORDER BY supplier_city;
This would return all records sorted by the supplier_city field in ascending order.
Example #2
SELECT supplier_city
FROM supplier
WHERE supplier_name = 'IBM'
ORDER BY supplier_city DESC;
This would return all records sorted by the supplier_city field in descending order.
Example #3
You can also sort by relative position in the result set, where the first field in the result set is 1. The next field is 2, and so on.
SELECT supplier_city
FROM supplier
WHERE supplier_name = 'IBM'
ORDER BY 1 DESC;
This would return all records sorted by the supplier_city field in descending order, since the supplier_city field is in position #1 in the result set.
Example #4
SELECT supplier_city, supplier_state
FROM supplier
WHERE supplier_name = 'IBM'
ORDER BY supplier_city DESC, supplier_state ASC;
This would return all records sorted by the supplier_city field in descending order, with a secondary sort by supplier_state in ascending order.
SQL: Joins
A join is used to combine rows from multiple tables. A join is performed whenever two or more tables is listed in the FROM clause of an SQL statement.
There are different kinds of joins. Let's take a look at a few examples.
Inner Join (simple join)
Chances are, you've already written an SQL statement that uses an inner join. It is is the most common type of join. Inner joins return all rows from multiple tables where the join condition is met.
For example,
SELECT suppliers.supplier_id, suppliers.supplier_name, orders.order_date
FROM suppliers, orders
WHERE suppliers.supplier_id = orders.supplier_id;
This SQL statement would return all rows from the suppliers and orders tables where there is a matching supplier_id value in both the suppliers and orders tables.
Let's look at some data to explain how inner joins work:
We have a table called suppliers with two fields (supplier_id and supplier_ name).
It contains the following data:
| supplier_id | supplier_name |
| 10000 | IBM |
| 10001 | Hewlett Packard |
| 10002 | Microsoft |
| 10003 | Nvidia |
We have another table called orders with three fields (order_id, supplier_id, and order_date).
It contains the following data:
| order_id | supplier_id | order_date |
| 500125 | 10000 | 2003/05/12 |
| 500126 | 10001 | 2003/05/13 |
If we ran the SQL statement below:
SELECT suppliers.supplier_id, suppliers.supplier_name, orders.order_date
FROM suppliers, orders
WHERE suppliers.supplier_id = orders.supplier_id;
Our result set would look like this:
| supplier_id | name | order_date |
| 10000 | IBM | 2003/05/12 |
| 10001 | Hewlett Packard | 2003/05/13 |
The rows for Microsoft and Nvidia from the supplier table would be omitted, since the supplier_id's 10002 and 10003 do not exist in both tables.
Outer Join
Another type of join is called an outer join. This type of join returns all rows from one table and only those rows from a secondary table where the joined fields are equal (join condition is met).
For example,
select suppliers.supplier_id, suppliers.supplier_name, orders.order_date
from suppliers, orders
where suppliers.supplier_id = orders.supplier_id(+);
This SQL statement would return all rows from the suppliers table and only those rows from the orders table where the joined fields are equal.
The (+) after the orders.supplier_id field indicates that, if a supplier_id value in the suppliers table does not exist in the orders table, all fields in the orders table will display as in the result set.
The above SQL statement could also be written as follows:
select suppliers.supplier_id, suppliers.supplier_name, orders.order_date
from suppliers, orders
where orders.supplier_id(+) = suppliers.supplier_id
Let's look at some data to explain how outer joins work:
We have a table called suppliers with two fields (supplier_id and name).
It contains the following data:
| supplier_id | supplier_name |
| 10000 | IBM |
| 10001 | Hewlett Packard |
| 10002 | Microsoft |
| 10003 | Nvidia |
We have a second table called orders with three fields (order_id, supplier_id, and order_date).
It contains the following data:
| order_id | supplier_id | order_date |
| 500125 | 10000 | 2003/05/12 |
| 500126 | 10001 | 2003/05/13 |
If we ran the SQL statement below:
select suppliers.supplier_id, suppliers.supplier_name, orders.order_date
from suppliers, orders
where suppliers.supplier_id = orders.supplier_id(+);
Our result set would look like this:
| supplier_id | supplier_name | order_date |
| 10000 | IBM | 2003/05/12 |
| 10001 | Hewlett Packard | 2003/05/13 |
| 10002 | Microsoft |
|
| 10003 | Nvidia |
|
The rows for Microsoft and Nvidia would be included because an outer join was used. However, you will notice that the order_date field for those records contains a value.
Oracle/PLSQL: Subqueries
What is a subquery?
A subquery is a query within a query. In Oracle, you can create subqueries within your SQL statements. These subqueries can reside in the WHERE clause, the FROM clause, or the SELECT clause.
WHERE clause
Most often, the subquery will be found in the WHERE clause. These subqueries are also called nested subqueries.
For example:
select * from all_tables tabs
where tabs.table_name in
(select cols.table_name
from all_tab_columns cols
where cols.column_name = 'SUPPLIER_ID');
Limitations: Oracle allows up to 255 levels of subqueries in the WHERE clause.
FROM clause
A subquery can also be found in the FROM clause. These are called inline views.
For example:
select suppliers.name, subquery1.total_amt
from suppliers,
(select supplier_id, Sum(orders.amount) as total_amt
from orders
group by supplier_id) subquery1,
where subquery1.supplier_id = suppliers.supplier_id;
In this example, we've created a subquery in the FROM clause as follows:
(select supplier_id, Sum(orders.amount) as total_amt
from orders
group by supplier_id) subquery1
This subquery has been aliased with the name subquery1. This will be the name used to reference this subquery or any of its fields.
Limitations: Oracle allows an unlimited number of subqueries in the FROM clause.
SELECT clause
A subquery can also be found in the SELECT clause.
For example:
select tbls.owner, tbls.table_name,
(select count(column_name) as total_columns
from all_tab_columns cols
where cols.owner = tbls.owner
and cols.table_name = tbls.table_name) subquery2
from all_tables tbls;
In this example, we've created a subquery in the SELECT clause as follows:
(select count(column_name) as total_columns
from all_tab_columns cols
where cols.owner = tbls.owner
and cols.table_name = tbls.table_name) subquery2
The subquery has been aliased with the name subquery2. This will be the name used to reference this subquery or any of its fields.
The trick to placing a subquery in the select clause is that the subquery must return a single value. This is why an aggregate function such as SUM, COUNT, MIN, or MAX is commonly used in the subquery.
SQL: UNION Query
The UNION query allows you to combine the result sets of 2 or more "select" queries. It removes duplicate rows between the various "select" statements.
Each SQL statement within the UNION query must have the same number of fields in the result sets with similar data types.
The syntax for a UNION query is:
select field1, field2, . field_n
from tables
UNION
select field1, field2, . field_n
from tables;
Example #1
The following is an example of a UNION query:
select supplier_id
from suppliers
UNION
select supplier_id
from orders;
In this example, if a supplier_id appeared in both the suppliers and orders table, it would appear once in your result set. The UNION removes duplicates.
Example #2 - With ORDER BY Clause
The following is a UNION query that uses an ORDER BY clause:
select supplier_id, supplier_name
from suppliers
where supplier_id > 2000
UNION
select company_id, company_name
from companies
where company_id > 1000
ORDER BY 2;
Since the column names are different between the two "select" statements, it is more advantageous to reference the columns in the ORDER BY clause by their position in the result set. In this example, we've sorted the results by supplier_name / company_name in ascending order, as denoted by the "ORDER BY 2".
The supplier_name / company_name fields are in position #2 in the result set.
Frequently Asked Questions
Question: I need to compare two dates and return the count of a field based on the date values. For example, I have a date field in a table called last updated date. I have to check if trunc(last_updated_date >= trun(sysdate-13).
Answer: Since you are using the COUNT function which is an aggregate function, we'd recommend using a UNION query. For example, you could try the following:
SELECT a.code as Code, a.name as Name, count(b.Ncode)
FROM cdmaster a, nmmaster b
WHERE a.code = b.code
and a.status = 1
and b.status = 1
and b.Ncode <> 'a10'
and trunc(last_updated_date) <= trunc(sysdate-13)
group by a.code, a.name
UNION
SELECT a.code as Code, a.name as Name, count(b.Ncode)
FROM cdmaster a, nmmaster b
WHERE a.code = b.code
and a.status = 1
and b.status = 1
and b.Ncode <> 'a10'
and trunc(last_updated_date) > trunc(sysdate-13)
group by a.code, a.name;
The UNION query allows you to perform a COUNT based on one set of criteria.
trunc(last_updated_date) <= trunc(sysdate-13)
As well as perform a COUNT based on another set of criteria.
trunc(last_updated_date) > trunc(sysdate-13)
SQL: UNION ALL Query
The UNION ALL query allows you to combine the result sets of 2 or more "select" queries. It returns all rows (even if the row exists in more than one of the "select" statements).
Each SQL statement within the UNION ALL query must have the same number of fields in the result sets with similar data types.
The syntax for a UNION ALL query is:
select field1, field2, . field_n
from tables
UNION ALL
select field1, field2, . field_n
from tables;
Example #1
The following is an example of a UNION ALL query:
select supplier_id
from suppliers
UNION ALL
select supplier_id
from orders;
If a supplier_id appeared in both the suppliers and orders table, it would appear multiple times in your result set. The UNION ALL does not remove duplicates.
Example #2 - With ORDER BY Clause
The following is a UNION query that uses an ORDER BY clause:
select supplier_id, supplier_name
from suppliers
where supplier_id > 2000
UNION ALL
select company_id, company_name
from companies
where company_id > 1000
ORDER BY 2;
Since the column names are different between the two "select" statements, it is more advantageous to reference the columns in the ORDER BY clause by their position in the result set. In this example, we've sorted the results by supplier_name / company_name in ascending order, as denoted by the "ORDER BY 2".
The supplier_name / company_name fields are in position #2 in the result set.
SQL: INTERSECT Query
The INTERSECT query allows you to return the results of 2 or more "select" queries. However, it only returns the rows selected by all queries. If a record exists in one query and not in the other, it will be omitted from the INTERSECT results.
Each SQL statement within the INTERSECT query must have the same number of fields in the result sets with similar data types.
The syntax for an INTERSECT query is:
select field1, field2, . field_n
from tables
INTERSECT
select field1, field2, . field_n
from tables;
Example #1
The following is an example of an INTERSECT query:
select supplier_id
from suppliers
INTERSECT
select supplier_id
from orders;
In this example, if a supplier_id appeared in both the suppliers and orders table, it would appear in your result set.
Example #2 - With ORDER BY Clause
The following is an INTERSECT query that uses an ORDER BY clause:
select supplier_id, supplier_name
from suppliers
where supplier_id > 2000
INTERSECT
select company_id, company_name
from companies
where company_id > 1000
ORDER BY 2;
Since the column names are different between the two "select" statements, it is more advantageous to reference the columns in the ORDER BY clause by their position in the result set. In this example, we've sorted the results by supplier_name / company_name in ascending order, as denoted by the "ORDER BY 2".
The supplier_name / company_name fields are in position #2 in the result set.
SQL: MINUS Query
The MINUS query returns all rows in the first query that are not returned in the second query.
Each SQL statement within the MINUS query must have the same number of fields in the result sets with similar data types.
The syntax for an MINUS query is:
select field1, field2, . field_n
from tables
MINUS
select field1, field2, . field_n
from tables;
Example #1
The following is an example of an MINUS query:
select supplier_id
from suppliers
MINUS
select supplier_id
from orders;
In this example, the SQL would return all supplier_id values that are in the suppliers table and not in the orders table. What this means is that if a supplier_id value existed in the suppliers table and also existed in the orders table, the supplier_id value would not appear in this result set.
Example #2 - With ORDER BY Clause
The following is an MINUS query that uses an ORDER BY clause:
select supplier_id, supplier_name
from suppliers
where supplier_id > 2000
MINUS
select company_id, company_name
from companies
where company_id > 1000
ORDER BY 2;
Since the column names are different between the two "select" statements, it is more advantageous to reference the columns in the ORDER BY clause by their position in the result set. In this example, we've sorted the results by supplier_name / company_name in ascending order, as denoted by the "ORDER BY 2".
The supplier_name / company_name fields are in position #2 in the result set.
SQL: UPDATE Statement
The UPDATE statement allows you to update a single record or multiple records in a table.
The syntax the UPDATE statement is:
UPDATE table
SET column = expression
WHERE predicates;
Example #1 - Simple example
Let's take a look at a very simple example.
UPDATE supplier
SET name = 'HP'
WHERE name = 'IBM';
This statement would update all supplier names in the supplier table from IBM to HP.
Example #2 - More complex example
You can also perform more complicated updates.
You may wish to update records in one table based on values in another table. Since you can't list more than one table in the UPDATE statement, you can use the EXISTS clause.
For example:
UPDATE supplier
SET supplier_name = ( SELECT customer.name
FROM customers
WHERE customers.customer_id = supplier.supplier_id)
WHERE EXISTS
( SELECT customer.name
FROM customers
WHERE customers.customer_id = supplier.supplier_id);
Whenever a supplier_id matched a customer_id value, the supplier_name would be overwritten to the customer name from the customers table.
SQL: INSERT Statement
The INSERT statement allows you to insert a single record or multiple records into a table.
The syntax for the INSERT statement is:
INSERT INTO table
(column-1, column-2, ... column-n)
VALUES
(value-1, value-2, ... value-n);
Example #1 - Simple example
Let's take a look at a very simple example.
INSERT INTO supplier
(supplier_id, supplier_name)
VALUES
(24553, 'IBM');
This would result in one record being inserted into the supplier table. This new record would have a supplier_id of 24553 and a supplier_name of IBM.
Example #2 - More complex example
You can also perform more complicated inserts using sub-selects.
For example:
INSERT INTO supplier
(supplier_id, supplier_name)
SELECT account_no, name
FROM customers
WHERE city = 'Newark';
By placing a "select" in the insert statement, you can perform multiples inserts quickly.
With this type of insert, you may wish to check for the number of rows being inserted. You can determine the number of rows that will be inserted by running the following SQL statement before performing the insert.
SELECT count(*)
FROM customers
WHERE city = 'Newark';
Frequently Asked Questions
Question: I am setting up a database with clients. I know that you use the "insert" statement to insert information in the database, but how do I make sure that I do not enter the same client information again?
Answer: You can make sure that you do not insert duplicate information by using the EXISTS condition.
For example, if you had a table named clients with a primary key of client_id, you could use the following statement:
INSERT INTO clients
(client_id, client_name, client_type)
SELECT supplier_id, supplier_name, 'advertising'
FROM suppliers
WHERE not exists (select * from clients
where clients.client_id = suppliers.supplier_id);
This statement inserts multiple records with a subselect.
If you wanted to insert a single record, you could use the following statement:
INSERT INTO clients
(client_id, client_name, client_type)
SELECT 10345, 'IBM', 'advertising'
FROM dual
WHERE not exists (select * from clients
where clients.client_id = 10345);
The use of the dual table allows you to enter your values in a select statement, even though the values are not currently stored in a table.
SQL: DELETE Statement
The DELETE statement allows you to delete a single record or multiple records from a table.
The syntax for the DELETE statement is:
DELETE FROM table
WHERE predicates;
Example #1 - Simple example
Let's take a look at a simple example:
DELETE FROM supplier
WHERE supplier_name = 'IBM';
This would delete all records from the supplier table where the supplier_name is IBM.
You may wish to check for the number of rows that will be deleted. You can determine the number of rows that will be deleted by running the following SQL statement before performing the delete.
SELECT count(*)
FROM supplier
WHERE supplier_name = 'IBM';
Example #2 - More complex example
You can also perform more complicated deletes.
You may wish to delete records in one table based on values in another table. Since you can't list more than one table in the FROM clause when you are performing a delete, you can use the EXISTS clause.
For example:
DELETE FROM supplier
WHERE EXISTS
( select customer.name
from customer
where customer.customer_id = supplier.supplier_id
and customer.customer_name = 'IBM' );
This would delete all records in the supplier table where there is a record in the customer table whose name is IBM, and the customer_id is the same as the supplier_id.
Learn more about the EXISTS condition.
If you wish to determine the number of rows that will be deleted, you can run the following SQL statement before performing the delete.
SELECT count(*) FROM supplier
WHERE EXISTS
( select customer.name
from customer
where customer.customer_id = supplier.supplier_id
and customer.customer_name = 'IBM' );
Frequently Asked Questions
Question: How would I write an SQL statement to delete all records in TableA whose data in field1 & field2 DO NOT match the data in fieldx & fieldz of TableB?
Answer: You could try something like this:
DELETE FROM TableA
WHERE NOT EXISTS
( select *
from TableB
where TableA .field1 = TableB.fieldx
and TableA .field2 = TableB.fieldz );
SQL Topics: Tables
CREATE Table
CREATE Table from another table
ALTER Table
DROP Table
Global Temporary tables
Local Temporary tables
SQL: CREATE Table
The basic syntax for a CREATE TABLE is:
CREATE TABLE table_name
(column1 datatype null/not null,
column2 datatype null/not null,
...
);
Each column must have a datatype. The column should either be defined as "null" or "not null" and if this value is left blank, the database assumes "null" as the default.
For example:
CREATE TABLE supplier
( supplier_id numeric(10) not null,
supplier_name varchar2(50) not null,
contact_name varchar2(50)
)
SQL: CREATE Table from another table
You can also create a table from an existing table by copying the existing table's columns.
It is important to note that when creating a table in this way, the new table will be populated with the records from the existing table (based on the SELECT Statement).
Syntax #1 - Copying all columns from another table
The basic syntax is:
CREATE TABLE new_table
AS (SELECT * FROM old_table);
For example:
CREATE TABLE suppliers
AS (SELECT *
FROM companies
WHERE id > 1000);
This would create a new table called suppliers that included all columns from the companies table.
If there were records in the companies table, then the new suppliers table would also contain the records selected by the SELECT statement.
Syntax #2 - Copying selected columns from another table
The basic syntax is:
CREATE TABLE new_table
AS (SELECT column_1, column2, ... column_n FROM old_table);
For example:
CREATE TABLE suppliers
AS (SELECT id, address, city, state, zip
FROM companies
WHERE id > 1000);
This would create a new table called suppliers, but the new table would only include the specified columns from the companies table.
Again, if there were records in the companies table, then the new suppliers table would also contain the records selected by the SELECT statement.
Syntax #3 - Copying selected columns from multiple tables
The basic syntax is:
CREATE TABLE new_table
AS (SELECT column_1, column2, ... column_n
FROM old_table_1, old_table_2, ... old_table_n);
For example:
CREATE TABLE suppliers
AS (SELECT companies.id, companies.address, categories.cat_type
FROM companies, categories
WHERE companies.id = categories.id
AND companies.id > 1000);
This would create a new table called suppliers based on columns from both the companies and categories tables.
Acknowledgements: We'd like to thank Dave M. for contributing to this solution!
SQL: ALTER Table
The ALTER TABLE command allows you to add, modify, or drop a column from an existing table.
Adding column(s) to a table
Syntax #1
To add a column to an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
ADD column_name column-definition;
For example:
ALTER TABLE supplier
ADD supplier_name varchar2(50);
This will add a column called supplier_name to the supplier table.
Syntax #2
To add multiple columns to an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
ADD ( column_1 column-definition,
column_2 column-definition,
...
column_n column_definition );
For example:
ALTER TABLE supplier
ADD (supplier_name varchar2(50),
city varchar2(45) );
This will add two columns (supplier_name and city) to the supplier table.
Modifying column(s) in a table
Syntax #1
To modify a column in an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
MODIFY column_name column_type;
For example:
ALTER TABLE supplier
MODIFY supplier_name varchar2(100) not null;
This will modify the column called supplier_name to be a data type of varchar2(100) and force the column to not allow null values.
Syntax #2
To modify multiple columns in an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
MODIFY (column_1 column_type,
column_2 column_type,
...
column_n column_type );
For example:
ALTER TABLE supplier
MODIFY (supplier_name varchar2(100) not null,
city varchar2(75));
This will modify both the supplier_name and city columns.
Drop column(s) in a table
Syntax #1
To drop a column in an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
DROP COLUMN column_name;
For example:
ALTER TABLE supplier
DROP COLUMN supplier_name;
This will drop the column called supplier_name from the table called supplier.
Rename column(s) in a table
(NEW in Oracle 9i Release 2)
Syntax #1
Starting in Oracle 9i Release 2, you can now rename a column.
To rename a column in an existing table, the ALTER TABLE syntax is:
ALTER TABLE table_name
RENAME COLUMN old_name to new_name;
For example:
ALTER TABLE supplier
RENAME COLUMN supplier_name to sname;
This will rename the column called supplier_name to sname.
Acknowledgements: Thanks to Dave M., Craig A., and Susan W. for contributing to this solution!
SQL: DROP Table
The basic syntax for a DROP TABLE is:
DROP TABLE table_name;
For example:
DROP TABLE supplier;
This would drop table called supplier.
SQL: Global Temporary tables
Global temporary tables are distinct within SQL sessions.
The basic syntax is:
CREATE GLOBAL TEMPORARY TABLE table_name ( ...);
For example:
CREATE GLOBAL TEMPORARY TABLE supplier
( supplier_id numeric(10) not null,
supplier_name varchar2(50) not null,
contact_name varchar2(50)
)
This would create a global temporary table called supplier .
SQL: Local Temporary tables
Local temporary tables are distinct within modules and embedded SQL programs within SQL sessions.
The basic syntax is:
DECLARE LOCAL TEMPORARY TABLE table_name ( ...);
SQL: VIEWS
A view is, in essence, a virtual table. It does not physically exist. Rather, it is created by a query joining one or more tables.
Creating a VIEW
The syntax for creating a VIEW is:
CREATE VIEW view_name AS
SELECT columns
FROM table
WHERE predicates;
For example:
CREATE VIEW sup_orders AS
SELECT supplier.supplier_id, orders.quantity, orders.price
FROM supplier, orders
WHERE supplier.supplier_id = orders.supplier_id
and supplier.supplier_name = 'IBM';
This would create a virtual table based on the result set of the select statement. You can now query the view as follows:
SELECT *
FROM sup_orders;
Updating a VIEW
You can update a VIEW without dropping it by using the following syntax:
CREATE OR REPLACE VIEW view_name AS
SELECT columns
FROM table
WHERE predicates;
For example:
CREATE or REPLACE VIEW sup_orders AS
SELECT supplier.supplier_id, orders.quantity, orders.price
FROM supplier, orders
WHERE supplier.supplier_id = orders.supplier_id
and supplier.supplier_name = 'Microsoft';
Dropping a VIEW
The syntax for dropping a VIEW is:
DROP VIEW view_name;
For example:
DROP VIEW sup_orders;
Frequently Asked Questions
Question: Can you update the data in a view?
Answer: A view is created by joining one or more tables. When you update record(s) in a view, it updates the records in the underlying tables that make up the view.
So, yes, you can update the data in a view providing you have the proper privileges to the underlying tables.
Oracle/PLSQL: Data Types
The following is a list of datatypes available in Oracle and PLSQL. We've tried to differentiate between datatypes available in Oracle 8i versus Oracle 9i.
| Data Type
Syntax | Oracle 8i | Oracle 9i | Explanation
(if applicable) |
| dec(p, s) | The maximum precision is 38 digits. | The maximum precision is 38 digits. | Where p is the precision and s is the scale. For example, dec(3,1) is a number that has 2 digits before the decimal and 1 digit after the decimal. |
| decimal(p, s) | The maximum precision is 38 digits. | The maximum precision is 38 digits. | Where p is the precision and s is the scale. For example, decimal(3,1) is a number that has 2 digits before the decimal and 1 digit after the decimal. |
| double precision | | | |
| float | | | |
| int | | | |
| integer | | | |
| numeric(p, s) | The maximum precision is 38 digits. | The maximum precision is 38 digits. | Where p is the precision and s is the scale. For example, numeric(7,2) is a number that has 5 digits before the decimal and 2 digits after the decimal. |
| number(p, s) | The maximum precision is 38 digits. | The maximum precision is 38 digits. | Where p is the precision and s is the scale. For example, number(7,2) is a number that has 5 digits before the decimal and 2 digits after the decimal. |
| real | | | |
| smallint | | | |
| char (size) | Up to 32767 bytes in PLSQL. Up to 2000 bytes in Oracle 8i. | Up to 32767 bytes in PLSQL. Up to 2000 bytes in Oracle 9i. | Where size is the number of characters to store. Fixed-length strings. Space padded. |
| varchar2 (size) | Up to 32767 bytes in PLSQL. Up to 4000 bytes in Oracle 8i. | Up to 32767 bytes in PLSQL. Up to 4000 bytes in Oracle 9i. | Where size is the number of characters to store. Variable-length strings. |
| long | Up to 2 gigabytes. | Up to 2 gigabytes. | Variable-length strings. (backward compatible) |
| raw | Up to 32767 bytes in PLSQL. Up to 2000 bytes in Oracle 8i. | Up to 32767 bytes in PLSQL. Up to 2000 bytes in Oracle 9i. | Variable-length binary strings |
| long raw | Up to 2 gigabytes. | Up to 2 gigabytes. | Variable-length binary strings. (backward compatible) |
| date | A date between Jan 1, 4712 BC and Dec 31, 9999 AD. | A date between Jan 1, 4712 BC and Dec 31, 9999 AD. | |
| timestamp (fractional seconds precision) | Not supported in Oracle 8i. | fractional seconds precision must be a number between 0 and 9. (default is 6) | Includes year, month, day, hour, minute, and seconds. For example:
timestamp(6) |
| timestamp (fractional seconds precision) with time zone | Not supported in Oracle 8i. | fractional seconds precision must be a number between 0 and 9. (default is 6) | Includes year, month, day, hour, minute, and seconds; with a time zone displacement value. For example:
timestamp(5) with time zone |
| timestamp (fractional seconds precision) with local time zone | Not supported in Oracle 8i. | fractional seconds precision must be a number between 0 and 9. (default is 6) | Includes year, month, day, hour, minute, and seconds; with a time zone expressed as the session time zone. For example:
timestamp(4) with local time zone |
| interval year
(year precision)
to month | Not supported in Oracle 8i. | year precision must be a number between 0 and 9. (default is 2) | Time period stored in years and months. For example:
interval year(4) to month |
| interval day
(day precision)
to second (fractional seconds precision) | Not supported in Oracle 8i. | day precision must be a number between 0 and 9. (default is 2) fractional seconds precision must be a number between 0 and 9. (default is 6) | Time period stored in days, hours, minutes, and seconds. For example:
interval day(2) to second(6) |
| rowid | The format of the rowid is:
BBBBBBB.RRRR.FFFFF Where BBBBBBB is the block in the database file;
RRRR is the row in the block;
FFFFF is the database file. | The format of the rowid is: BBBBBBB.RRRR.FFFFF Where BBBBBBB is the block in the database file;
RRRR is the row in the block;
FFFFF is the database file. | Fixed-length binary data. Every record in the database has a physical address or rowid. |
| urowid [size] | Up to 2000 bytes. | Up to 2000 bytes. | Universal rowid. Where size is optional. |
| boolean | Valid in PLSQL, but this datatype does not exist in Oracle 8i. | Valid in PLSQL, but this datatype does not exist in Oracle 9i. | |
| nchar (size) | Up to 32767 bytes in PLSQL. Up to 2000 bytes in Oracle 8i | Up to 32767 bytes in PLSQL. Up to 2000 bytes in Oracle 9i. | Where size is the number of characters to store. Fixed-length NLS string |
| nvarchar2 (size) | Up to 32767 bytes in PLSQL. Up to 4000 bytes in Oracle 8i. | Up to 32767 bytes in PLSQL. Up to 4000 bytes in Oracle 9i. | Where size is the number of characters to store. Variable-length NLS string |
| bfile | Up to 4 gigabytes. | Up to 4 gigabytes. | File locators that point to a read-only binary object outside of the database |
| blob | U p to 4 gigabytes. | Up to 4 gigabytes. | LOB locators that point to a large binary object within the database |
| clob | Up to 4 gigabytes. | Up to 4 gigabytes. | LOB locators that point to a large character object within the database |
| nclob | Up to 4 gigabytes. | Up to 4 gigabytes. | LOB locators that point to a large NLS character object within the database |
Oracle/PLSQL: Literals
A literal is the same as a constant. We'll cover three types of literals - text literals, integer literals, and number literals
Text literals are always surrounded by single quotes ('). For example:
'Hewlett Packard'
'28-MAY-03'
Integer literals can be up to 38 digits. Integer literals can be either positive numbers or negative numbers. If you do not specify a sign, then a positive number is assumed. Here are some examples of valid integer literals:
23
+23
-23
Number literals can be up to 38 digits. Number literals can be either positive or negative numbers. If you do not specify a sign, then a positive number is assumed. Here are some examples of valid number literals:
25
+25
-25
25e-04
25.607
Oracle/PLSQL: Declaring Variables
The syntax for declaring variables is:
variable_name datatype [CONSTANT] [NOT NULL] [:= | DEFAULT initial_value]
For example:
Declaring a variable:
LDescription varchar2(40);
Declaring a constant:
LTotal constant numeric(8,1) := 8363934.1;
Declaring a variable with an initial value (not a constant):
LType varchar2(10) := 'Example';
Oracle/PLSQL: IS NULL
In other languages, a null value is found using the = null syntax. However in PLSQL to check if a value is null, you must use the "IS NULL" syntax.
To check for equality on a null value, you must use "IS NULL".
For example,
IF Lvalue IS NULL then
.
END IF;
If Lvalue contains a null value, the "IF" expression will evaluate to TRUE.
You can also use "IS NULL" in an SQL statement. For example:
select * from suppliers
where supplier_name IS NULL;
This will return all records from the suppliers table where the supplier_name contains a null value.
To learn how to check for a value that is not null, click here.
Oracle/PLSQL: IS NOT NULL
In other languages, a not null value is found using the != null syntax. However in PLSQL to check if a value is not null, you must use the "IS NOT NULL" syntax.
For example,
IF Lvalue IS NOT NULL then
.
END IF;
If Lvalue does not contain a null value, the "IF" expression will evaluate to TRUE.
You can also use "IS NOT NULL" in an SQL statement. For example:
select * from suppliers
where supplier_name IS NOT NULL;
This will return all records from the suppliers table where the supplier_name does not contain a null value.
To learn how to check for a value that is null, click here.
