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Add a comment to update_ref_and_keys

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2005-04-14 17:47:48 -07:00
parent 9b583225b3
commit e35244d626
1 changed files with 7 additions and 3 deletions
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10
sql/sql_select.cc
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@ -3161,10 +3161,14 @@ update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
}
/*
Special treatment for ft-keys.
Remove the following things from KEYUSE:
Sort the array of possible keys and remove the following key parts:
- ref if there is a keypart which is a ref and a const.
- keyparts without previous keyparts.
(e.g. if there is a key(a,b) and the clause is a=3 and b=7 and b=t2.d,
then we skip the key part corresponding to b=t2.d)
- keyparts without previous keyparts
(e.g. if there is a key(a,b,c) but only b < 5 (or a=2 and c < 3) is
used in the query, we drop the partial key parts from consideration).
Special treatment for ft-keys.
*/
if (keyuse->elements)
{