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MDEV-17017 Explain for query using derived table specified with a table

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value constructor shows wrong number of rows

If the specification of a derived table contained a table value constructor
then the optimizer incorrectly estimated the number of rows in the derived
table. This happened because the optimizer did not take into account the
number of rows in the constructor. The wrong estimate could lead to choosing
inefficient execution plans.
This commit is contained in:
Igor Babaev
2018-08-18 22:57:20 -07:00
parent 0dadb96e16
commit a1fd25c22b
9 changed files with 115 additions and 23 deletions
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57
mysql-test/main/table_value_constr.result
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@@ -2097,3 +2097,60 @@ v
#
with t as (values (),()) select 1 from t;
ERROR HY000: Row with no elements is not allowed in table value constructor in this context
#
# MDEV-17017: TVC in derived table
#
create table t1 (a int);
insert into t1 values (9), (3), (2);
select * from (values (7), (5), (8), (1), (3), (8), (1)) t;
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explain select * from (values (7), (5), (8), (1), (3), (8), (1)) t;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 7
2 DERIVED NULL NULL NULL NULL NULL NULL NULL No tables used
select * from (values (1,11), (7,77), (3,31), (4,42)) t;
1 11
1 11
7 77
3 31
4 42
explain select * from (values (1,11), (7,77), (3,31), (4,42)) t;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 4
2 DERIVED NULL NULL NULL NULL NULL NULL NULL No tables used
select * from (values (7), (5), (8), (1) union values (3), (8), (1)) t;
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explain select * from (values (7), (5), (8), (1) union values (3), (8), (1)) t;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 7
2 DERIVED NULL NULL NULL NULL NULL NULL NULL No tables used
3 UNION NULL NULL NULL NULL NULL NULL NULL No tables used
NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
select * from (values (7), (5), (8), (1) union select * from t1) t;
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explain select * from (values (7), (5), (8), (1) union select * from t1) t;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 7
2 DERIVED NULL NULL NULL NULL NULL NULL NULL No tables used
3 UNION t1 ALL NULL NULL NULL NULL 3
NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
drop table t1;