Before Postgres insert data, it follow rules we defined: Constraints. There are many constraints in Postgres:
- CHECK constraints — to enforce data correctness
- Foreign Key constraints — to enforce integrity across tables
- UNIQUE constraints — to enforce uniqueness of every row
Example: CHECK constraint
A very common use case is to use
CHECK constraint to enforce
NOT NULL on an existing column will block all reads and writes until every row is checked.
Add a CHECK constraint but not validate first.
Validate the constraint.
Then add the
Remove the CHECK constraint.