SQLite

The query in the SQL below gets a different answer after the index is
created.  The answer without the index is correct.

<blockquote><verbatim>
CREATE TABLE t1(a, b);  INSERT INTO t1 VALUES(1,2);
CREATE TABLE t2(x, y);  INSERT INTO t2 VALUES(1,3);
SELECT y FROM t1, t2 WHERE a=x AND b<=y ORDER BY b DESC;
CREATE INDEX t1ab ON t1(a,b);
SELECT y FROM t1, t2 WHERE a=x AND b<=y ORDER BY b DESC;
</verbatim></blockquote>

This problem appears to have been introduced by check-in [559733b09e] on
2016-05-20, 572 days ago.  The problem first appeared in version 3.14.0.
The problem was discovered in the wild and reported to the SQLite developers
via private email.

Incorrect result when an index is used for an ordered join