The snippet library.
Small, practical examples. Search by task or narrow things down below.
Apply a default when an insert omits a column
Postgres: A default supplies an omitted value; an explicit NULL still follows the column’s nullability rules.
Postgres✓ Tested
Block deletion of a referenced parent
Postgres: The default foreign-key action prevents deletion while a child still refers to the parent.
Postgres✓ Tested
Enforce a bounded numeric range
Postgres: A named CHECK constraint keeps numeric values inside an inclusive interval.
Postgres✓ Tested
Keep children while clearing a deleted relationship
Postgres: ON DELETE SET NULL requires a nullable foreign-key column.
Postgres✓ Tested
Make a pair of columns unique together
Postgres: A composite primary key permits repeated individual values while forbidding a duplicate combination.
Postgres✓ Tested
Reference a parent identified by two columns
Postgres: A composite foreign key checks the complete referenced key rather than either column independently.
Postgres✓ Tested
Reject a negative quantity with CHECK
Postgres: Combine NOT NULL and CHECK because an unknown NULL check result is normally accepted.
Postgres✓ Tested
Reject duplicate business identifiers
Postgres: A UNIQUE constraint protects a business key independently of the primary key.
Postgres✓ Tested
Remove dependent rows with a declared cascade
Postgres: ON DELETE CASCADE removes children when their referenced parent is deleted.
Postgres✓ Tested
Require a value with NOT NULL
Postgres: Declare required fields at the database boundary, not only in application validation.
Postgres✓ Tested