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Ticket UUID: d805526eae253103dc307740dcf859b6d701c2f4
Title: Incorrect join result or assertion fault due to transitive constraints
Status: Fixed Type: Code_Defect
Severity: Severe Priority: Immediate
Subsystem: Unknown Resolution: Fixed
Last Modified: 2013-07-08 21:13:16
Version Found In: 3.7.17
User Comments:
drh added on 2013-07-08 18:02:53:

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.

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.