From 5ca1ee5eea4d08491772388f39a664e21df32b9b Mon Sep 17 00:00:00 2001 From: unknown Date: Wed, 26 Jul 2006 13:32:28 +0300 Subject: [PATCH] Bug #21019: First result of SELECT COUNT(*) different than consecutive runs When optimizing conditions like 'a = OR a IS NULL' so that they're united into a single condition on the key and checked together the server must check which value is the NULL value in a correct way : not only using ->is_null but also check if the expression doesn't depend on any tables referenced in the current statement. This additional check must be performed because that optimization takes place before the actual execution of the statement, so if the field was initialized to NULL from a previous statement the optimization would be applied incorrectly. mysql-test/r/select.result: Bug #21019: First result of SELECT COUNT(*) different than consecutive runs - test case mysql-test/t/select.test: Bug #21019: First result of SELECT COUNT(*) different than consecutive runs - test case. Note that ALTER TABLE is important here : it happens to leave the Field instance for t1.b set to NULL, witch is vital for demonstrating the problem fixed by this changeset. sql/sql_select.cc: Bug #21019: First result of SELECT COUNT(*) different than consecutive runs - check whether a value is null taking into account its table dependency. --- mysql-test/r/select.result | 26 ++++++++++++++++++++++++++ mysql-test/t/select.test | 15 +++++++++++++++ sql/sql_select.cc | 7 +++++-- 3 files changed, 46 insertions(+), 2 deletions(-) diff --git a/mysql-test/r/select.result b/mysql-test/r/select.result index c7df11ab018..d415c336715 100644 --- a/mysql-test/r/select.result +++ b/mysql-test/r/select.result @@ -2744,3 +2744,29 @@ SELECT i='1e+01',i=1e+01, i in (1e+01), i in ('1e+01') FROM t1; i='1e+01' i=1e+01 i in (1e+01) i in ('1e+01') 0 1 1 1 DROP TABLE t1; +CREATE TABLE t1 (a int, b int); +INSERT INTO t1 VALUES (1,1), (2,1), (4,10); +CREATE TABLE t2 (a int PRIMARY KEY, b int, KEY b (b)); +INSERT INTO t2 VALUES (1,NULL), (2,10); +ALTER TABLE t1 ENABLE KEYS; +EXPLAIN SELECT STRAIGHT_JOIN SQL_NO_CACHE COUNT(*) FROM t2, t1 WHERE t1.b = t2.b OR t2.b IS NULL; +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t2 index b b 5 NULL 2 Using index +1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using where +SELECT STRAIGHT_JOIN SQL_NO_CACHE * FROM t2, t1 WHERE t1.b = t2.b OR t2.b IS NULL; +a b a b +1 NULL 1 1 +1 NULL 2 1 +1 NULL 4 10 +2 10 4 10 +EXPLAIN SELECT STRAIGHT_JOIN SQL_NO_CACHE COUNT(*) FROM t2, t1 WHERE t1.b = t2.b OR t2.b IS NULL; +id select_type table type possible_keys key key_len ref rows Extra +1 SIMPLE t2 index b b 5 NULL 2 Using index +1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using where +SELECT STRAIGHT_JOIN SQL_NO_CACHE * FROM t2, t1 WHERE t1.b = t2.b OR t2.b IS NULL; +a b a b +1 NULL 1 1 +1 NULL 2 1 +1 NULL 4 10 +2 10 4 10 +DROP TABLE IF EXISTS t1,t2; diff --git a/mysql-test/t/select.test b/mysql-test/t/select.test index 4cdfc220350..23fc09b5e39 100644 --- a/mysql-test/t/select.test +++ b/mysql-test/t/select.test @@ -2297,4 +2297,19 @@ INSERT INTO t1 VALUES (10); SELECT i='1e+01',i=1e+01, i in (1e+01), i in ('1e+01') FROM t1; DROP TABLE t1; +# +# Bug #21019: First result of SELECT COUNT(*) different than consecutive runs +# +CREATE TABLE t1 (a int, b int); +INSERT INTO t1 VALUES (1,1), (2,1), (4,10); + +CREATE TABLE t2 (a int PRIMARY KEY, b int, KEY b (b)); +INSERT INTO t2 VALUES (1,NULL), (2,10); +ALTER TABLE t1 ENABLE KEYS; + +EXPLAIN SELECT STRAIGHT_JOIN SQL_NO_CACHE COUNT(*) FROM t2, t1 WHERE t1.b = t2.b OR t2.b IS NULL; +SELECT STRAIGHT_JOIN SQL_NO_CACHE * FROM t2, t1 WHERE t1.b = t2.b OR t2.b IS NULL; +EXPLAIN SELECT STRAIGHT_JOIN SQL_NO_CACHE COUNT(*) FROM t2, t1 WHERE t1.b = t2.b OR t2.b IS NULL; +SELECT STRAIGHT_JOIN SQL_NO_CACHE * FROM t2, t1 WHERE t1.b = t2.b OR t2.b IS NULL; +DROP TABLE IF EXISTS t1,t2; # End of 4.1 tests diff --git a/sql/sql_select.cc b/sql/sql_select.cc index fd8a5149edd..77ad0b8b163 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -2143,8 +2143,11 @@ merge_key_fields(KEY_FIELD *start,KEY_FIELD *new_fields,KEY_FIELD *end, /* field = expression OR field IS NULL */ old->level= and_level; old->optimize= KEY_OPTIMIZE_REF_OR_NULL; - /* Remember the NOT NULL value */ - if (old->val->is_null()) + /* + Remember the NOT NULL value unless the value does not depend + on other tables. + */ + if (!old->val->used_tables() && old->val->is_null()) old->val= new_fields->val; /* The referred expression can be NULL: */ old->null_rejecting= 0;