PostgreSQL SyntaxLesson 39Free preview

PostgreSQL EXISTS

This lesson is part of PostgreSQL · All levels

Summary

EXISTS is a predicate operator that checks whether a subquery returns at least one line. If there is a line, the result is TRUE; if not, FALSE. Varian NOT EXIST is used to find rows that have no relation whatsoever, and this type of subquery often correlates with external queries.

Key points

EXISTS is valued TRUE when the subquery produces at least one line.
NOT EXIST is the opposite of looking for the absence of a relationship.
Subqueries often correlate with external query columns.
The execution stops once one line is found so efficiently.

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