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BUG#22393: Very wrong E(#rows(ref(const)) for key with skewed distribution

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- Check if we have E(#rows) for 'range' access on the smaller interval 
  on the same index. If yes, adjust the estimate.


mysql-test/r/range.result:
  BUG#22393: Testcase
mysql-test/t/range.test:
  BUG#22393: Testcase
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2006-09-18 14:49:54 +04:00
parent b128cfa851
commit 5e34af3240
3 changed files with 64 additions and 0 deletions
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14
mysql-test/r/range.result
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@ -896,3 +896,17 @@ EXPLAIN SELECT * FROM t1 WHERE 0 NOT BETWEEN b AND c;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge idx1,idx2 idx1,idx2 4,4 NULL 4 Using sort_union(idx1,idx2); Using where
DROP TABLE t1;
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, filler char(100));
insert into t2 select A.a + 10 * (B.a + 10 * C.a), 10, 'filler' from t1 A,
t1 B, t1 C where A.a < 5;
insert into t2 select 1000, b, 'filler' from t2;
alter table t2 add index (a,b);
select 'In following EXPLAIN the access method should be ref, #rows~=500 (and not 2)' Z;
Z
In following EXPLAIN the access method should be ref, #rows~=500 (and not 2)
explain select * from t2 where a=1000 and b<11;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ref a a 5 const 502 Using where
drop table t1, t2;