#At lp:maria based on revid:psergey@askmonty.org-20090608135546-ut1yrzbah4gdw6e6 2711 Sergey Petrunia 2009-06-10 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(). modified: mysql-test/r/ps_11bugs.result mysql-test/r/subselect.result mysql-test/r/table_elim.result mysql-test/t/table_elim.test sql/item.h sql/item_sum.cc sql/item_sum.h per-file messages: 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 === modified file 'mysql-test/r/ps_11bugs.result' --- a/mysql-test/r/ps_11bugs.result 2008-10-08 11:23:53 +0000 +++ b/mysql-test/r/ps_11bugs.result 2009-06-09 21:11:33 +0000 @@ -121,8 +121,8 @@ insert into t1 values (1); explain select * from t1 where 3 in (select (1+1) union select 1); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables -2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL No tables used -3 DEPENDENT UNION NULL NULL NULL NULL NULL NULL NULL No tables used +2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible HAVING +3 DEPENDENT UNION NULL NULL NULL NULL NULL NULL NULL Impossible HAVING NULL UNION RESULT ALL NULL NULL NULL NULL NULL select * from t1 where 3 in (select (1+1) union select 1); a === modified file 'mysql-test/r/subselect.result' --- a/mysql-test/r/subselect.result 2009-04-25 09:04:38 +0000 +++ b/mysql-test/r/subselect.result 2009-06-09 21:11:33 +0000 @@ -4353,13 +4353,13 @@ id select_type table type possible_keys 1 PRIMARY t1 ALL NULL NULL NULL NULL 2 100.00 2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort Warnings: -Note 1003 select 1 AS `1` from `test`.`t1` where (1,<exists>(select 1 AS `1` from `test`.`t1` group by `test`.`t1`.`a` having (<cache>(1) = (1)))) +Note 1003 select 1 AS `1` from `test`.`t1` where (1,<exists>(select 1 AS `1` from `test`.`t1` group by `test`.`t1`.`a` having 1)) EXPLAIN EXTENDED SELECT 1 FROM t1 WHERE 1 IN (SELECT 1 FROM t1 WHERE a > 3 GROUP BY a); id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables 2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 2 100.00 Using where; Using temporary; Using filesort Warnings: -Note 1003 select 1 AS `1` from `test`.`t1` where (1,<exists>(select 1 AS `1` from `test`.`t1` where (`test`.`t1`.`a` > 3) group by `test`.`t1`.`a` having (<cache>(1) = (1)))) +Note 1003 select 1 AS `1` from `test`.`t1` where (1,<exists>(select 1 AS `1` from `test`.`t1` where (`test`.`t1`.`a` > 3) group by `test`.`t1`.`a` having 1)) DROP TABLE t1; End of 5.0 tests. CREATE TABLE t1 (a INT, b INT); === modified file 'mysql-test/r/table_elim.result' --- a/mysql-test/r/table_elim.result 2009-06-03 13:10:45 +0000 +++ b/mysql-test/r/table_elim.result 2009-06-09 21:11:33 +0000 @@ -53,4 +53,19 @@ t3.a=t1.a) on t0.a=t1.a; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t0 ALL NULL NULL NULL NULL 4 1 SIMPLE t1 ALL NULL NULL NULL NULL 4 +# Elimination with aggregate functions +explain select count(*) from t1 left join t2 on t2.a=t1.a; +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t1 ALL NULL NULL NULL NULL 4 +explain select count(1) from t1 left join t2 on t2.a=t1.a; +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t1 ALL NULL NULL NULL NULL 4 +explain select count(1) from t1 left join t2 on t2.a=t1.a group by t1.a; +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t1 ALL NULL NULL NULL NULL 4 Using temporary; Using filesort +This must not use elimination: +explain select count(1) from t1 left join t2 on t2.a=t1.a group by t2.a; +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t1 ALL NULL NULL NULL NULL 4 Using temporary; Using filesort +1 SIMPLE t2 eq_ref PRIMARY PRIMARY 4 test.t1.a 1 Using index drop table t0, t1, t2, t3; === modified file 'mysql-test/t/table_elim.test' --- a/mysql-test/t/table_elim.test 2009-06-03 13:10:45 +0000 +++ b/mysql-test/t/table_elim.test 2009-06-09 21:11:33 +0000 @@ -29,8 +29,6 @@ explain select t1.a from t1 left join t2 --echo # This will not be eliminated as t2.b is in group list: explain select t1.a from t1 left join t2 on t2.a=t1.a group by t2.b; -## TODO: Aggregate functions prevent table elimination ATM. - --echo # This will not be eliminated as t2.b is in the WHERE explain select t1.a from t1 left join t2 on t2.a=t1.a where t2.b < 3 or t2.b is null; @@ -47,6 +45,13 @@ from t0 left join (t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and t3.a=t1.a) on t0.a=t1.a; +--echo # Elimination with aggregate functions +explain select count(*) from t1 left join t2 on t2.a=t1.a; +explain select count(1) from t1 left join t2 on t2.a=t1.a; +explain select count(1) from t1 left join t2 on t2.a=t1.a group by t1.a; + +--echo This must not use elimination: +explain select count(1) from t1 left join t2 on t2.a=t1.a group by t2.a; drop table t0, t1, t2, t3; === modified file 'sql/item.h' --- a/sql/item.h 2009-04-25 10:05:32 +0000 +++ b/sql/item.h 2009-06-09 21:11:33 +0000 @@ -2203,6 +2203,10 @@ public: if (!depended_from) (*ref)->update_used_tables(); } + bool const_item() const + { + return (*ref)->const_item(); + } table_map not_null_tables() const { return (*ref)->not_null_tables(); } void set_result_field(Field *field) { result_field= field; } bool is_result_field() { return 1; } === modified file 'sql/item_sum.cc' --- a/sql/item_sum.cc 2009-04-25 09:04:38 +0000 +++ b/sql/item_sum.cc 2009-06-09 21:11:33 +0000 @@ -542,11 +542,6 @@ void Item_sum::update_used_tables () args[i]->update_used_tables(); used_tables_cache|= args[i]->used_tables(); } - - used_tables_cache&= PSEUDO_TABLE_BITS; - - /* the aggregate function is aggregated into its local context */ - used_tables_cache |= (1 << aggr_sel->join->tables) - 1; } } === modified file 'sql/item_sum.h' --- a/sql/item_sum.h 2008-12-09 19:43:10 +0000 +++ b/sql/item_sum.h 2009-06-09 21:11:33 +0000 @@ -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()