How to drop constraints in postgres?

Question

I have this query in SQL:

IF EXISTS (SELECT * FROM dbo.sysobjects WHERE id = object_id('[FK_states_list]') AND OBJECTPROPERTY(id, 'IsForeignKey') = 1) ALTER TABLE [custom_table] DROP CONSTRAINT [FK_states_list] ; 

How can I write this query in Postgres?

Answer 1

It seems you want to drop the constraint, only if it exists.

In Postgres you can use:

ALTER TABLE custom_table    DROP CONSTRAINT IF EXISTS fk_states_list; 

You can also make sure the table exists:

ALTER TABLE IF EXISTS custom_table    DROP CONSTRAINT IF EXISTS fk_states_list;