NULL

The absence of a value. NULL is not a type you declare — it appears when a column has no value or an expression produces no result.

Comparisons

This type does not support direct comparisons with =, <, or >. Extract or cast values first.

Notes

NULL is never equal to anything, including itself. Use IS NULL or IS NOT NULL to test for nulls. NULL propagates through arithmetic and most functions: 1 + NULL is NULL.

Limitations

• You cannot CAST to NULL.
• NULL = NULL evaluates to NULL (unknown, per SQL three-valued logic) — not TRUE and not FALSE. It never matches in a WHERE clause, which looks like FALSE from the outside, but the value itself is NULL; use IS NULL instead.