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Merge polly.(none):/home/kaa/src/opt/bug32202/my51-bug26215

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into  polly.(none):/home/kaa/src/opt/mysql-5.1-opt
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kaa@polly.(none)
2007-11-10 22:48:17 +03:00
parent 0fe103f90f 9e829a56d4
commit ed2ae869d9
3 changed files with 113 additions and 4 deletions
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17
sql/sql_select.cc
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@ -1081,10 +1081,19 @@ JOIN::optimize()
We have found that grouping can be removed since groups correspond to
only one row anyway, but we still have to guarantee correct result
order. The line below effectively rewrites the query from GROUP BY
<fields> to ORDER BY <fields>. One exception is if skip_sort_order is
set (see above), then we can simply skip GROUP BY.
*/
order= skip_sort_order ? 0 : group_list;
<fields> to ORDER BY <fields>. There are two exceptions:
- if skip_sort_order is set (see above), then we can simply skip
GROUP BY;
- we can only rewrite ORDER BY if the ORDER BY fields are 'compatible'
with the GROUP BY ones, i.e. either one is a prefix of another.
We only check if the ORDER BY is a prefix of GROUP BY. In this case
test_if_subpart() copies the ASC/DESC attributes from the original
ORDER BY fields.
If GROUP BY is a prefix of ORDER BY, then it is safe to leave
'order' as is.
*/
if (!order || test_if_subpart(group_list, order))
order= skip_sort_order ? 0 : group_list;
/*
If we have an IGNORE INDEX FOR GROUP BY(fields) clause, this must be
rewritten to IGNORE INDEX FOR ORDER BY(fields).