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author | Sergey Petrunia <psergey@askmonty.org> | 2009-06-10 01:11:33 +0400 |
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committer | Sergey Petrunia <psergey@askmonty.org> | 2009-06-10 01:11:33 +0400 |
commit | fd485ad9889f2d8db6a2de6c61efb720cb97e96a (patch) | |
tree | f462823874fbcb7842e5dabe052c8b376323d1c1 /sql/item_sum.h | |
parent | cf028a54746d6b166e9ffe8fa1e2e08569fe0dc1 (diff) | |
download | mariadb-git-fd485ad9889f2d8db6a2de6c61efb720cb97e96a.tar.gz |
MWL#17: Table elimination
- Make elimination work with aggregate functions. The problem was that aggregate functions
reported all table bits in used_tables(), and that prevented table elimination. Fixed by
making aggregate functions return more correct value from used_tables().
mysql-test/r/ps_11bugs.result:
MWL#17: Table elimination
- Update test results. The difference is because of Item_ref change: outer references to constants
are now recognized as constants, too.
mysql-test/r/subselect.result:
- Update test results. The difference is because of Item_ref change: outer references to constants
are now recognized as constants, too.
mysql-test/r/table_elim.result:
MWL#17: Table elimination
- Check that elimination works in presense of aggreagate functions
mysql-test/t/table_elim.test:
MWL#17: Table elimination
- Check that elimination works in presense of aggreagate functions
sql/item.h:
MWL#17: Table elimination
- Add Item_ref::const_item() which calls (*ref)->const_item(). Before this diff Item_ref used the
default implementation of const_item(){ return used_tables()==0; }. This is no longer true, as
COUNT(*) now has used_tables()==0 but const_item()==FALSE.
sql/item_sum.cc:
MWL#17: Table elimination
- Make Item_sum() and it descendants not to return all bits in used_tables(). This is needed
because otherwise table elimination can't work in presense of aggregate functions
- COUNT(*) now has used_tables()==0 and const_item()==FALSE. Had to change
Item_ref::const_item() to account for this.
sql/item_sum.h:
MWL#17: Table elimination
- Add comments
Diffstat (limited to 'sql/item_sum.h')
-rw-r--r-- | sql/item_sum.h | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/sql/item_sum.h b/sql/item_sum.h index d991327d847..aec5830f381 100644 --- a/sql/item_sum.h +++ b/sql/item_sum.h @@ -255,6 +255,12 @@ protected: */ Item **orig_args, *tmp_orig_args[2]; table_map used_tables_cache; + + /* + TRUE <=> We've managed to calculate the value of this Item in + opt_sum_query(), hence it can be considered constant at all subsequent + steps. + */ bool forced_const; public: @@ -341,6 +347,14 @@ public: virtual const char *func_name() const= 0; virtual Item *result_item(Field *field) { return new Item_field(field); } + /* + Return bitmap of tables that are needed to evaluate the item. + + The implementation takes into account the used strategy: items resolved + at optimization phase report 0. + Items that depend on the number of rows only, e.g. COUNT(*) will report + zero, but will still false from const_item(). + */ table_map used_tables() const { return used_tables_cache; } void update_used_tables (); void cleanup() |