Details
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Type:
Bug
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Status: Closed
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Priority:
Major
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Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: None
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Component/s: None
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Labels:
Description
The following test case (for LP BUG#609121) extracted from subselect_mat.test:
create table t1 (c1 int);
create table t2 (c2 int);
insert into t1 values (1);
insert into t2 values (2);
SELECT SUM(c1) c1_sum FROM t1 WHERE c1 IN (SELECT c2 FROM t2) HAVING c1_sum;
incorrectly produces a NULL instead of an empty result.
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Re: Empty query with SUM and HAVING, no GROUP BY returns NULL instead of empty result.
Analysis:
Close to its end JOIN::optimize() assigns having to tmp_having, and
sets the having clause to NULL:
tmp_having= having;
if (select_options & SELECT_DESCRIBE)
having= 0;
At the same time, this query detects an empty result set, and calls
return_zero_rows(), which must check the HAVING clause by:
if (having && having->val_int() == 0)
send_row=0;
However having has been already set to NULL, so return_zero_rows
doesn't check the having clause, hence the wrong result.
Solution:
There are two ways to solve this problem:
a) check join->tmp_having in addition to join->having, or
b) do not set having= 0 in JOIN::optimize.
Launchpad bug id: 702345
Re: Empty query with SUM and HAVING, no GROUP BY returns NULL instead of empty result.
The bug is present both with MATERIALIZATION and with IN-TO-EXISTS,
but not with SEMIJOIN:
set @@optimizer_switch='materialization=on,in_to_exists=on,semijoin=off';
set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=off';
set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';