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BUG#14940: Slow join order is chosen: [2nd commit with post-review fixes]

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- Re-worked the prev_record_reads() function to return the lower bound of
  number of different table access scans that will be performed.
This commit is contained in:
sergefp@mysql.com
2006-09-29 15:58:47 +04:00
parent 16a5d97a5d
commit 47b357522a
4 changed files with 161 additions and 13 deletions
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28
mysql-test/r/join.result
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@@ -776,3 +776,31 @@ id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL a,b NULL NULL NULL 1000 Using where
1 SIMPLE t3 ref b b 5 test.t2.b 1 Using where
drop table t1, t2, t3;
create table t1 (a int);
insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t2 (a int, b int, primary key(a));
insert into t2 select @v:=A.a+10*B.a, @v from t1 A, t1 B;
explain select * from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 10
show status like '%cost%';
Variable_name Value
Last_query_cost 4.016090
select 'The cost of accessing t1 (dont care if it changes' '^';
The cost of accessing t1 (dont care if it changes
The cost of accessing t1 (dont care if it changes^
select 'vv: Following query must use ALL(t1), eq_ref(A), eq_ref(B): vv' Z;
Z
vv: Following query must use ALL(t1), eq_ref(A), eq_ref(B): vv
explain select * from t1, t2 A, t2 B where A.a = t1.a and B.a=A.b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 10
1 SIMPLE A eq_ref PRIMARY PRIMARY 4 test.t1.a 1
1 SIMPLE B eq_ref PRIMARY PRIMARY 4 test.A.b 1
show status like '%cost%';
Variable_name Value
Last_query_cost 24.016090
select '^^: The above should be ~= 20 + cost(select * from t1). Value less than 20 is an error' Z;
Z
^^: The above should be ~= 20 + cost(select * from t1). Value less than 20 is an error
drop table t1, t2;