The transform_null_equals configuration in Postgres

It is a well-known fact that you should always use IS NULL to test if some value is null. That is because NULL = NULL does not evaluate to true in SQL, instead it evaluates to NULL.

However, if you insist on violating SQL standards and making NULL = NULL be true, you can. There's a runtime configuration option for that: transform_null_equals (docs).

SELECT NULL = NULL;
-- Returns NULL

SET transform_null_equals TO true;

SELECT NULL = NULL;
-- Returns TRUE

Should you use this option? No.

This only works for specifically = NULL constructions. In particular, NULL != NULL will still return NULL instead of FALSE, and NULL IN (1, NULL, 2) will not return TRUE, even with the option enabled. But it's there if you need it.

transform_null_equals is off by default, and is available in all versions of Postgres.