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Fix for BUG#20954: avg(keyval) retuns 0.38 but max(keyval) returns an empty set

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The problem was in that opt_sum_query() replaced MIN/MAX functions
with the corresponding constant found in a key, but due to imprecise
representation of float numbers, when evaluating the where clause,
this comparison failed.

When MIN/MAX optimization detects that all tables can be removed,
also remove all conjuncts in a where clause that refer to these
tables. As a result of this fix, these conditions are not evaluated
twice, and in the case of float number comparisons we do not discard
result rows due to imprecise float representation.

As a side-effect this fix also corrects an unnoticed problem in
bug 12882.
This commit is contained in:
timour/timka@lamia.home
2006-07-26 01:11:19 +03:00
parent bffd438de3
commit 86ae2f3b06
5 changed files with 100 additions and 1 deletions
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mysql-test/r/subselect.result
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@@ -539,7 +539,7 @@ EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
Warnings:
Note 1003 select max(test.t1.numreponse) AS `MAX(numreponse)` from test.t1 where (test.t1.numeropost = _latin1'1')
Note 1003 select max(test.t1.numreponse) AS `MAX(numreponse)` from test.t1
EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 const PRIMARY,numreponse PRIMARY 7 const,const 1 Using index