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BUG#16798: Merge into 5.0: s/used_tables()/!const_item()/, added comment about its effects.

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2006-05-07 19:01:49 +04:00
parent c23774128a
commit 5b09d7a5e1
1 changed files with 14 additions and 2 deletions
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16
sql/sql_select.cc
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@ -2377,7 +2377,19 @@ merge_key_fields(KEY_FIELD *start,KEY_FIELD *new_fields,KEY_FIELD *end,
{
if (old->field == new_fields->field)
{
if (new_fields->val->used_tables())
/*
NOTE: below const_item() call really works as "!used_tables()", i.e.
it can return FALSE where it is feasible to make it return TRUE.
The cause is as follows: Some of the tables are already known to be
const tables (the detection code is in make_join_statistics(),
above the update_ref_and_keys() call), but we didn't propagate
information about this: TABLE::const_table is not set to TRUE, and
Item::update_used_tables() hasn't been called for each item.
The result of this is that we're missing some 'ref' accesses.
TODO: OptimizerTeam: Fix this
*/
if (!new_fields->val->const_item())
{
/*
If the value matches, we can use the key reference.
@ -2407,7 +2419,7 @@ merge_key_fields(KEY_FIELD *start,KEY_FIELD *new_fields,KEY_FIELD *end,
new_fields->null_rejecting);
}
else if (old->eq_func && new_fields->eq_func &&
((!old->val->used_tables() && old->val->is_null()) ||
((old->val->const_item() && old->val->is_null()) ||
new_fields->val->is_null()))
{
/* field = expression OR field IS NULL */