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Data & databasesGuide

PostgreSQL foreign keys: NO ACTION timing and selective SET NULL

A closer look at explicitly deferred NO ACTION checks and clearing only the optional component of a composite foreign key. These details complement the basic choice between RESTRICT, CASCADE and SET NULL.

postgresql / foreign-key / on-delete / data-retention / cascade / restrict / set-null / referential-integrity

Data & databasesGuide

Choose a PostgreSQL foreign-key deletion policy without losing the wrong rows

Compare RESTRICT, CASCADE and SET NULL using a small isolated example, then check the actual constraint and dependent rows before changing real data.

PostgreSQL / SQL / Foreign keys / Transactions

Data & databasesGuide

Why SQL comparisons with NULL do not behave like zero

Understand IS NULL, three-valued logic and the difference between COUNT(*) and COUNT(column).

SQL / PostgreSQL / NULL