SQLite

The following SQL generates a single row of output where it should generate an empty set:

CREATE TABLE t1(a INTEGER PRIMARY KEY);
INSERT INTO t1(a) VALUES(1),(2);
CREATE TABLE t2(b INTEGER PRIMARY KEY);
INSERT INTO t2(b) VALUES(1);
SELECT a FROM t1 WHERE a NOT IN (SELECT a FROM t2);

Apparently, the subquery "(SELECT a FROM t2)" is being compiled as if it where "(SELECT b FROM t2)". This problem appears to go back to before version 3.6.1, circa 2008.

Problem reported at stackoverflow and relayed to the sqlite-users mailing list by Clemens Ladisch.