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Fix bug#11482 4.1.12 produces different resultset for a complex query

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than in previous 4.1.x

Wrongly applied optimization were adding NOT NULL constraint which results in
rejecting valid rows and reduced result set.

The problem was that add_notnull_conds() while checking subquery were adding
NOT NULL constraint to left joined table, to which, normally, optimization 
don't have to be applied.
This commit is contained in:
evgen@moonbone.local 2005-07-18 18:30:19 +04:00
parent b144b920a0
commit 6e9447a80e
3 changed files with 41 additions and 1 deletions
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11
mysql-test/r/select.result
View file

@ -2559,3 +2559,14 @@ WHERE
COUNT(*)
4
drop table t1,t2,t3;
create table t1 (f1 int);
insert into t1 values (1),(NULL);
create table t2 (f2 int, f3 int, f4 int);
create index idx1 on t2 (f4);
insert into t2 values (1,2,3),(2,4,6);
select A.f2 from t1 left join t2 A on A.f2 = f1 where A.f3=(select min(f3)
from t2 C where A.f4 = C.f4) or A.f3 IS NULL;
f2
1
NULL
drop table t1,t2;

11
mysql-test/t/select.test
View file

@ -2116,3 +2116,14 @@ WHERE
drop table t1,t2,t3;
#
# Bug #11482 4.1.12 produces different resultset for a complex query
# than in previous 4.1.x
create table t1 (f1 int);
insert into t1 values (1),(NULL);
create table t2 (f2 int, f3 int, f4 int);
create index idx1 on t2 (f4);
insert into t2 values (1,2,3),(2,4,6);
select A.f2 from t1 left join t2 A on A.f2 = f1 where A.f3=(select min(f3)
from t2 C where A.f4 = C.f4) or A.f3 IS NULL;
drop table t1,t2;

20
sql/sql_select.cc
View file

@ -3508,7 +3508,23 @@ inline void add_cond_and_fix(Item **e1, Item *e2)
(where othertbl is a non-const table and othertbl.field may be NULL)
and add them to conditions on correspoding tables (othertbl in this
example).
Exception from that is the case when referred_tab->join != join.
I.e. don't add NOT NULL constraints from any embedded subquery.
Consider this query:
SELECT A.f2 FROM t1 LEFT JOIN t2 A ON A.f2 = f1
WHERE A.f3=(SELECT MIN(f3) FROM t2 C WHERE A.f4 = C.f4) OR A.f3 IS NULL;
Here condition A.f3 IS NOT NULL is going to be added to the WHERE
condition of the embedding query.
Another example:
SELECT * FROM t10, t11 WHERE (t10.a < 10 OR t10.a IS NULL)
AND t11.b <=> t10.b AND (t11.a = (SELECT MAX(a) FROM t12
WHERE t12.b = t10.a ));
Here condition t10.a IS NOT NULL is going to be added.
In both cases addition of NOT NULL condition will erroneously reject
some rows of the result set.
referred_tab->join != join constraint would disallow such additions.
This optimization doesn't affect the choices that ref, range, or join
optimizer make. This was intentional because this was added after 4.1
was GA.
@ -3539,6 +3555,8 @@ static void add_not_null_conds(JOIN *join)
DBUG_ASSERT(item->type() == Item::FIELD_ITEM);
Item_field *not_null_item= (Item_field*)item;
JOIN_TAB *referred_tab= not_null_item->field->table->reginfo.join_tab;
if (referred_tab->join != join)
continue;
Item *notnull;
if (!(notnull= new Item_func_isnotnull(not_null_item)))
DBUG_VOID_RETURN;