PostgreSQL Alter table drop check constraint from a table

To drop a check constraint from a table in PostgreSQL, you can use the ALTER TABLE statement. The ALTER TABLE statement is used to modify the structure of an existing table in the database. Here’s the syntax to drop a check constraint from a table:


ALTER TABLE table_name
DROP CONSTRAINT constraint_name;

Let’s break down the syntax:

ALTER TABLE: This clause is used to indicate that you want to alter the structure of a table.
table_name: Specifies the name of the table from which you want to drop the check constraint.
DROP CONSTRAINT: This clause is used to drop a constraint from the table.
constraint_name: Specifies the name of the check constraint that you want to drop.


Here’s an example to illustrate how to drop a check constraint from a table:

Suppose we have a table called employees with a check constraint named age_constraint that ensures the age column should be greater than or equal to 18:

CREATE TABLE employees (
  id serial PRIMARY KEY,
  name varchar(100),
  age integer CHECK (age >= 18)

To drop the age_constraint check constraint from the employees table, you can use the following SQL statement:

ALTER TABLE employees
DROP CONSTRAINT age_constraint;

After executing the above statement, the check constraint age_constraint will be removed from the employees table, and there will be no restriction on the minimum age for the employees.

It’s important to note that when dropping a check constraint, PostgreSQL verifies that the constraint is not referenced by other objects. If there are dependent objects, such as foreign key constraints or views, you’ll need to drop them or modify them accordingly before you can drop the check constraint successfully.

Remember to exercise caution when altering the structure of your database tables, as it can have a significant impact on your data integrity and application functionality. Always backup your data and test your changes thoroughly in a controlled environment before applying them to a production database.