Check Constraints - (Oracle Misc)

In Oracle, check constraints are used to ensure that the values in a column or set of columns meet a certain specified condition. The check constraint is enforced on insert or update operations against the table.

Syntax

The basic syntax for creating a check constraint in Oracle is as follows:

ALTER TABLE table_name
ADD CONSTRAINT constraint_name CHECK (condition);

Here, table_name is the name of the table for which we want to create the check constraint, constraint_name is the name of the constraint, and condition is the condition that must be met for the check constraint to succeed.

Example

Suppose we have a table called "employees" with columns "employee_id", "first_name", "last_name", and "age", and we want to create a check constraint to ensure that the age of each employee is greater than or equal to 18. We can create the check constraint using the following SQL statement:

ALTER TABLE employees
ADD CONSTRAINT check_age CHECK (age >= 18);

Output

If we try to insert a record into the "employees" table with an age less than 18, the check constraint will fail and we will receive an error message.

Explanation

In the above example, we have created a check constraint called "check_age" on the "age" column of the "employees" table. The condition for the check constraint is that the "age" column must be greater than or equal to 18. This ensures that we do not enter any invalid data into the table.

Use

Check constraints are useful for ensuring data integrity in a database. They can help to prevent invalid data from being inserted into a table, which can cause issues with queries and data analysis.

Important Points

• Check constraints are used to ensure that the values in a column or set of columns meet a certain specified condition.
• Check constraints are enforced on insert or update operations against the table.
• Check constraints are created using the ALTER TABLE command.
• Check constraints help ensure data integrity in a database.

Summary

In summary, check constraints in Oracle are an important tool for ensuring data integrity in a database. They can help to prevent invalid data from being inserted into a table, which can cause issues with queries and data analysis. Check constraints are easy to create using the ALTER TABLE command and can help to improve the overall quality of a database.