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MDEV-28285 Unexpected result when combining DISTINCT, subselect and LIMIT

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The problem was that when  JOIN_TAB::remove_duplicates() noticed there
can only be one possible row in the output, it adjusted limits but
didn't take into account any possible offset.

Fixed by not adjusting limit offset when setting one-row-limit.
This commit is contained in:
Monty
2023-05-22 18:58:45 +03:00
parent cd37e49422
commit 92d2ceac73
4 changed files with 56 additions and 1 deletions
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25
mysql-test/main/distinct.result
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@ -1157,3 +1157,28 @@ explain select * from t1 limit 0 offset 10;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Zero limit
drop table t1, t2;
#
# MDEV-28285 Unexpected result when combining DISTINCT, subselect
# and LIMIT
#
create table t1 (a int primary key);
create table t2 (a int primary key, b int not null);
insert into t1 select seq from seq_1_to_10;
insert into t2 select seq,seq from seq_1_to_10;
select distinct a from t1 where t1.a=1 and t1.a in (select a from t2 where t2.b in (1,2));
a
1
explain select distinct a from t1 where t1.a=1 and t1.a in (select a+0 from t2 where t2.b in (1,2)) limit 10,10;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 const PRIMARY PRIMARY 4 const 1 Using index; Using temporary
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 8 func 1
2 MATERIALIZED t2 ALL NULL NULL NULL NULL 10 Using where
select distinct a from t1 where t1.a=1 and t1.a in (select a+0 from t2 where t2.b in (1,2)) limit 10,10;
a
select distinct a from t1 where t1.a=1 and t1.a in (select a+0 from t2 where t2.b in (1,2)) limit 0,1;
a
1
drop table t1,t2;
#
# end of 10.5 tests
#