The following SQL should return a single row of result.  But due to the
transitive constraint optimization, it either hits an assertion fault or
it returns zero rows (depending on whether the SQLITE_DEBUG compile-time option
is used.)  Note that SQLITE_ENABLE_STAT3 is required for this bug to appear.

<blockquote><verbatim>
CREATE TABLE t1(w INTEGER PRIMARY KEY, x);
CREATE TABLE t2(y INTEGER, z);
INSERT INTO t1 VALUES(1,2);
INSERT INTO t2 VALUES(1,3);
SELECT *
  FROM t1 CROSS JOIN t2
 WHERE w=y AND y IS NOT NULL;


The problem appears to have been introduced by check-in [38852f158ab].

Low-level technical details:  The "y IS NOT NULL" constraint is translated
into a "y>NULL" virtual constraint when SQLITE_ENABLE_STAT3 is defined.
The y>NULL constraint tagged to indicate that the usual not-NULL check on
the right-hand side should be
skipped since this is an artificial constraint.  The normal index handler
knows to check for that tag and skip the not-NULL check.  But after the
transitive constraints were added, there is now also a "w>NULL" virtual
constraint (because w=x).  The w>NULL constraint is also tagged, but the
INTEGER PRIMARY KEY handlers does not know to check for that tag and to
skip the not-NULL check.  It sees that the right-hand side of the constraint
is NULL and all fails the constraint, resulting in no output rows.