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NULL

A special marker in SQL representing 'unknown' or 'missing' data, distinct from zero or an empty string. It follows three-valued logic in operations and produces special behavior in aggregation, filtering, joins, and other contexts.

Timeline (last 90 days)

Sep 12

In SQL's three-valued logic, the result of any comparison operation involving NULL is UNKNOWN, rather than TRUE or FALSE.

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Sep 12

In PostgreSQL, SELECT NULL = NULL returns NULL rather than TRUE.

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All Facts (2)

Unverified

In SQL's three-valued logic, the result of any comparison operation involving NULL is UNKNOWN, rather than TRUE or FALSE.

50%Unverified

In PostgreSQL, SELECT NULL = NULL returns NULL rather than TRUE.

50%

Source Articles

NULL in PostgreSQL: Computation Pitfalls and Handling StrategiesSep 12