revision-id: ebc5a2b917829363dcc9499523f249c87f990123 (mariadb-10.2.39-33-gebc5a2b9178) parent(s): 8147d2e6183a1a4a4f3db2884966f5da2d17678c author: Sergei Petrunia committer: Sergei Petrunia timestamp: 2021-06-30 13:47:01 +0300 message: MDEV-25969: Condition pushdown into derived table doesn't work if select list uses SP Variant 3, the "handle failures at conversion" approach. Consider a query in form: select ... from (select item2 as COL1) as T where COL1=123 Condition pushdown into derived table will try to push "COL1=123" condition down into table T. The process of pushdown involves "substituting" the item, that is, replacing Item_field("T.COL1") with its "producing item" item2. In order to use item2, one needs to clone it (call Item::build_clone). If the item is not cloneable (e.g. Item_func_sp is not), the pushdown process will fail and nothing at all will be pushed. Fixed by introducing transform_condition_or_part() which will try to apply the transformation for as many parts of condition as possible. The parts of condition that couldn't be transformed are dropped. --- mysql-test/r/derived_cond_pushdown.result | 146 ++++++++++++++++++++++++++++++ mysql-test/t/derived_cond_pushdown.test | 70 ++++++++++++++ sql/sql_derived.cc | 78 ++++++++++++++-- 3 files changed, 288 insertions(+), 6 deletions(-) diff --git a/mysql-test/r/derived_cond_pushdown.result b/mysql-test/r/derived_cond_pushdown.result index 28532ae88a4..f5ef3c3a84d 100644 --- a/mysql-test/r/derived_cond_pushdown.result +++ b/mysql-test/r/derived_cond_pushdown.result @@ -10673,4 +10673,150 @@ Warnings: Note 1003 select `v2`.`a` AS `a`,`v2`.`f` AS `f`,`v2`.`g` AS `g` from `test`.`v2` where `v2`.`f` = `v2`.`a` and `v2`.`g` = `v2`.`a` drop view v1,v2; drop table t1; +# +# MDEV-25969: Condition pushdown into derived table doesn't work if select list uses SP +# +create function f1(a int) returns int DETERMINISTIC return (a+1); +create table t1 ( +pk int primary key, +a int, +b int, +key(a) +); +create table t2(a int); +insert into t2 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9); +create table t3(a int); +insert into t3 select A.a + B.a* 10 + C.a * 100 from t2 A, t2 B, t2 C; +insert into t1 select a,a,a from t3; +create view v1 as +select +t1.a as col1, +f1(t1.b) as col2 +from +t1; +create view v2 as +select +t1.a as col1, +f1(t1.b) as col2 +from +t1; +create view v3 as +select col2, col1 from v1 +union all +select col2, col1 from v2; +explain select * from v3 where col1=123; +id select_type table type possible_keys key key_len ref rows Extra +1 PRIMARY <derived2> ALL NULL NULL NULL NULL 2 Using where +2 DERIVED t1 ref a a 5 const 1 +3 UNION t1 ref a a 5 const 1 +# This must use ref accesses for reading table t1, not full scans: +explain format=json +select * from v3 where col1=123 and col2=321; +EXPLAIN +{ + "query_block": { + "select_id": 1, + "table": { + "table_name": "<derived2>", + "access_type": "ALL", + "rows": 2, + "filtered": 100, + "attached_condition": "v3.col1 = 123 and v3.col2 = 321", + "materialized": { + "query_block": { + "union_result": { + "table_name": "<union2,3>", + "access_type": "ALL", + "query_specifications": [ + { + "query_block": { + "select_id": 2, + "table": { + "table_name": "t1", + "access_type": "ref", + "possible_keys": ["a"], + "key": "a", + "key_length": "5", + "used_key_parts": ["a"], + "ref": ["const"], + "rows": 1, + "filtered": 100 + } + } + }, + { + "query_block": { + "select_id": 3, + "table": { + "table_name": "t1", + "access_type": "ref", + "possible_keys": ["a"], + "key": "a", + "key_length": "5", + "used_key_parts": ["a"], + "ref": ["const"], + "rows": 1, + "filtered": 100 + } + } + } + ] + } + } + } + } + } +} +drop function f1; +drop view v1,v2,v3; +drop table t1, t2,t3; +# +# Another testcase, with pushdown through GROUP BY +# +create table t1 (a int, b int); +insert into t1 values (1,1),(2,2),(3,3); +create function f1(a int) returns int DETERMINISTIC return (a+1); +create view v2(a, a2, s) as +select a, f1(a), sum(b) from t1 group by a, f1(a); +# Here, +# "(s+1) > 10" will be pushed into HAVING +# "a > 1" will be pushed all the way to the table scan on t1 +# "a2>123" will be pushed into HAVING (as it refers to an SP call which +# prevents pushing it to the WHERE) +explain format=json +select * from v2 where (s+1) > 10 AND a > 1 and a2>123; +EXPLAIN +{ + "query_block": { + "select_id": 1, + "table": { + "table_name": "<derived2>", + "access_type": "ALL", + "rows": 3, + "filtered": 100, + "attached_condition": "v2.s + 1 > 10 and v2.a > 1 and v2.a2 > 123", + "materialized": { + "query_block": { + "select_id": 2, + "having_condition": "s + 1 > 10 and a2 > 123", + "filesort": { + "sort_key": "t1.a, f1(t1.a)", + "temporary_table": { + "table": { + "table_name": "t1", + "access_type": "ALL", + "rows": 3, + "filtered": 100, + "attached_condition": "t1.a > 1" + } + } + } + } + } + } + } +} +drop view v2; +drop function f1; +drop table t1; # End of 10.2 tests diff --git a/mysql-test/t/derived_cond_pushdown.test b/mysql-test/t/derived_cond_pushdown.test index 58f38ac1e5a..9b7658a725e 100644 --- a/mysql-test/t/derived_cond_pushdown.test +++ b/mysql-test/t/derived_cond_pushdown.test @@ -2237,4 +2237,74 @@ eval explain extended $q2; drop view v1,v2; drop table t1; +--echo # +--echo # MDEV-25969: Condition pushdown into derived table doesn't work if select list uses SP +--echo # +create function f1(a int) returns int DETERMINISTIC return (a+1); + +create table t1 ( + pk int primary key, + a int, + b int, + key(a) +); + +create table t2(a int); +insert into t2 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9); + +create table t3(a int); +insert into t3 select A.a + B.a* 10 + C.a * 100 from t2 A, t2 B, t2 C; + +insert into t1 select a,a,a from t3; + +create view v1 as +select + t1.a as col1, + f1(t1.b) as col2 +from + t1; + +create view v2 as +select + t1.a as col1, + f1(t1.b) as col2 +from + t1; +create view v3 as +select col2, col1 from v1 +union all +select col2, col1 from v2; + +explain select * from v3 where col1=123; + +--echo # This must use ref accesses for reading table t1, not full scans: +explain format=json +select * from v3 where col1=123 and col2=321; + +drop function f1; +drop view v1,v2,v3; +drop table t1, t2,t3; + +--echo # +--echo # Another testcase, with pushdown through GROUP BY +--echo # +create table t1 (a int, b int); +insert into t1 values (1,1),(2,2),(3,3); + +create function f1(a int) returns int DETERMINISTIC return (a+1); + +create view v2(a, a2, s) as +select a, f1(a), sum(b) from t1 group by a, f1(a); + +--echo # Here, +--echo # "(s+1) > 10" will be pushed into HAVING +--echo # "a > 1" will be pushed all the way to the table scan on t1 +--echo # "a2>123" will be pushed into HAVING (as it refers to an SP call which +--echo # prevents pushing it to the WHERE) +explain format=json +select * from v2 where (s+1) > 10 AND a > 1 and a2>123; + +drop view v2; +drop function f1; +drop table t1; --echo # End of 10.2 tests diff --git a/sql/sql_derived.cc b/sql/sql_derived.cc index 632baf4bc5b..4ee95eb0516 100644 --- a/sql/sql_derived.cc +++ b/sql/sql_derived.cc @@ -1192,6 +1192,67 @@ bool mysql_derived_reinit(THD *thd, LEX *lex, TABLE_LIST *derived) } +/* + @brief + Given condition cond and transformer+argument, try transforming as many + disjuncts as possible. + + @detail + The motivation of this function is to convert the condition that's being + pushed into a WHERE clause with derived_field_transformer_for_where. + The transformer may fail for some sub-condition, in this case we want to + convert the most restrictive part of the condition that's possible + + This function only does it for top-level AND: disjuncts that could not be + converted are dropped. + + @return + Converted condition, or NULL if nothing could be converted +*/ + +static +Item *transform_condition_or_part(THD *thd, + Item *cond, + Item_transformer transformer, + uchar *arg) +{ + if (cond->type() != Item::COND_ITEM || + ((Item_cond*) cond)->functype() != Item_func::COND_AND_FUNC) + { + Item *new_item= cond->transform(thd, transformer, arg); + // Indicate that the condition is not pushable + if (!new_item) + cond->clear_extraction_flag(); + return new_item; + } + + List_iterator<Item> li(*((Item_cond*) cond)->argument_list()); + Item *item; + while ((item=li++)) + { + Item *new_item= item->transform(thd, transformer, arg); + if (!new_item) + { + // Indicate that the condition is not pushable + item->clear_extraction_flag(); + li.remove(); + } + else + li.replace(new_item); + } + + switch (((Item_cond*) cond)->argument_list()->elements) + { + case 0: + return NULL; + case 1: + return ((Item_cond*) cond)->argument_list()->head(); + default: + return cond; + } +} + + /** @brief Extract the condition depended on derived table/view and pushed it there @@ -1287,9 +1348,11 @@ bool pushdown_cond_for_derived(THD *thd, Item *cond, TABLE_LIST *derived) if (!sl->join->group_list && !sl->with_sum_func) { /* extracted_cond_copy is pushed into where of sl */ - extracted_cond_copy= extracted_cond_copy->transform(thd, - &Item::derived_field_transformer_for_where, - (uchar*) sl); + extracted_cond_copy= + transform_condition_or_part(thd, + extracted_cond_copy, + &Item::derived_field_transformer_for_where, + (uchar*)sl); if (extracted_cond_copy) { extracted_cond_copy->walk( @@ -1316,9 +1379,12 @@ bool pushdown_cond_for_derived(THD *thd, Item *cond, TABLE_LIST *derived) pushed into the where clause of sl to make them usable in the new context */ if (cond_over_grouping_fields) - cond_over_grouping_fields= cond_over_grouping_fields->transform(thd, - &Item::derived_grouping_field_transformer_for_where, - (uchar*) sl); + { + cond_over_grouping_fields= + transform_condition_or_part(thd, cond_over_grouping_fields, + &Item::derived_grouping_field_transformer_for_where, + (uchar*) sl); + } if (cond_over_grouping_fields) {