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;


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.