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MWL#17: Table elimination

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- Do not show eliminated tables in the output of EXPLAIN EXTENDED
This commit is contained in:
Sergey Petrunia
2009-06-14 14:01:10 +04:00
parent fd485ad988
commit 402e58cf78
5 changed files with 45 additions and 16 deletions
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15
mysql-test/r/table_elim.result
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@ -10,6 +10,11 @@ as select a, a as b from t1 where a in (1,3);
explain select t1.a 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 extended select t1.a from t1 left join t2 on t2.a=t1.a;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4 100.00
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` where 1
select t1.a from t1 left join t2 on t2.a=t1.a;
a
0
@ -45,14 +50,16 @@ explain select t1.a from t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4
# Elimination when done within an outer join nest:
explain
explain extended
select t0.*
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;
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
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 4 100.00
1 SIMPLE t1 ALL NULL NULL NULL NULL 4 100.00
Warnings:
Note 1003 select `test`.`t0`.`a` AS `a` from `test`.`t0` left join (`test`.`t1`) on((`test`.`t0`.`a` = `test`.`t1`.`a`)) where 1
# 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