The incorrect result HASH / MERGE JOIN in the fields of type VARCHAR with a
trailing space
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Key: CORE-4909
URL: http://tracker.firebirdsql.org/browse/CORE-4909
Project: Firebird Core
Issue Type: Bug
Affects Versions: 3.0 Beta 2, 2.5.4
Reporter: Simonov Denis
RECREATE TABLE T (
V VARCHAR(10),
X INTEGER
);
INSERT INTO T (V, X) VALUES ('ww', 1);
INSERT INTO T (V, X) VALUES ('ww ', 2);
COMMIT;
--CREATE INDEX IDX_T_V ON T(V); -- If you remove the comment behavior changes
select
REPLACE(T1.V, ' ', '0') AS V1,
T1.X AS X1,
REPLACE(T2.V, ' ', '0') AS V2,
T2.X AS X2
from T T1 join T T2 on T1.V = T2.V
Firebird 3.0 Beta 2
PLAN HASH (T2 NATURAL, T1 NATURAL)
V1 X1 V2 X2
ww 1 ww 1
ww0 2 ww0 2
Firebird 2.5.5
PLAN MERGE (SORT (T2 NATURAL), SORT (T1 NATURAL))
V1 X1 V2 X2
ww 1 ww 1
ww0 2 ww0 2
Is replaced by the LEFT JOIN. There is only the optimizer can use NESTED LOOP
select
REPLACE(T1.V, ' ', '0') AS V1,
T1.X AS X1,
REPLACE(T2.V, ' ', '0') AS V2,
T2.X AS X2
from T T1 left join T T2 on T1.V = T2.V
Firebird 3.0 Beta 2 AND 2.5.5
PLAN JOIN (T1 NATURAL, T2 NATURAL)
V1 X1 V2 X2
ww 1 ww 1
ww 1 ww0 2
ww0 2 ww 1
ww0 2 ww0 2
If you uncomment the creation of the index, the result is the same as for a
LEFT JOIN, well, except for the plan.
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