Code Inspection: Redundant row limiting in queries

Reports redundant row limiting clauses like FETCH and LIMIT in queries.

Example (PostgreSQL):

CREATE TABLE foo(a INT);

SELECT * FROM foo WHERE EXISTS(SELECT * FROM foo LIMIT 2);
SELECT * FROM foo WHERE EXISTS(SELECT * FROM foo FETCH FIRST 2 ROWS ONLY);

To fix the warning, you can add OFFSET to limiting clauses. If OFFSET is missing, then LIMIT is redundant because the usage of LIMIT does not influence the operation result of EXISTS. In case with OFFSET, we skip first N rows and this will influence the output.

SELECT * FROM foo WHERE EXISTS(SELECT * FROM foo OFFSET 1 ROW LIMIT 2);
SELECT * FROM foo WHERE EXISTS(SELECT * FROM foo OFFSET 1 ROW FETCH FIRST 2 ROWS ONLY);

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Last modified: 13 May 2022