Details
-
Type:
Bug
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Status: Closed
-
Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: None
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Component/s: None
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Labels:
Description
This query:
SELECT *
FROM (
SELECT *
FROM t3
WHERE t3.b <= 'c'
) AS alias1
RIGHT JOIN t1
ON t1.a = alias1.b
AND ( 6 ) IN (
SELECT a
FROM t2
)
crashes when executed with derived_merge=ON, semijoin=ON and prepared statement.
explain:
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
3 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
optimizer switch: derived_merge=ON,semijoin=ON
full switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,index_condition_pushdown=off,derived_merge=on,derived_with_keys=off,firstmatch=off,loosescan=off,materialization=off,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on
test case:
CREATE TABLE t1 ( a varchar(1)) ;
CREATE TABLE t2 ( a int(11), b int(11)) ;
CREATE TABLE t3 ( a int(11) NOT NULL , b varchar(1)) ;
SET SESSION optimizer_switch = 'derived_merge=on';
SET SESSION optimizer_switch = 'semijoin=on';
PREPARE st1 from "
SELECT *
FROM (
SELECT *
FROM t3
WHERE t3.b <= 0
) AS alias1
RIGHT JOIN t1
ON t1.a = alias1.b
AND ( 6 ) IN (
SELECT a
FROM t2
)";
EXECUTE st1;
bzr version-info
revision-id: <email address hidden>
date: 2011-10-19 21:01:42 +0200
build-date: 2011-10-20 13:09:07 +0300
revno: 3242
branch-nick: maria-5.3
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Re: Assertion `0' failed in replace_where_subcondition with derived_merge and first execution of prepared statement
Test case without subquery in the ON clause:
CREATE TABLE t1 ( b int(11)) ;
CREATE TABLE t2 (c int, b int, d varchar(52) NOT NULL ) ;
CREATE TABLE t3 (b int(11)) ;
SET SESSION optimizer_switch='semijoin=on,derived_merge=on';
PREPARE st1 FROM '
SELECT * FROM t1
JOIN (
SELECT t2.* FROM t2
WHERE t2.d <> "a"
AND t2.c IN (
SELECT t3.b
FROM t3
)
) AS alias2
ON ( alias2.b = t1.b );
';
EXECUTE st1;
Re: Assertion `0' failed in replace_where_subcondition with derived_merge and first execution of prepared statement
The crash happens inside convert_join_subqueries_to_semijoins(). replace_where_subcondition() throws an assert, because it was unable to locate the subquery item that it needs to replace.
Re: Assertion `0' failed in replace_where_subcondition with derived_merge and first execution of prepared statement
The code goes like this:
Item **tree= (in_subq->emb_on_expr_nest == NO_JOIN_NEST)?
&join->conds : &(in_subq->emb_on_expr_nest->on_expr);
Item *replace_me= in_subq->original_item();
if (replace_where_subcondition(join, tree, replace_me, substitute,
do_fix_fields))
DBUG_RETURN(TRUE);
...
if (!thd->stmt_arena->is_conventional())
{ tree= (in_subq->emb_on_expr_nest == NO_JOIN_NEST)? &join->select_lex->prep_where : &(in_subq->emb_on_expr_nest->prep_on_expr); if (*tree && replace_where_subcondition(join, tree, replace_me, substitute, FALSE)) DBUG_RETURN(TRUE); }the assert happens inside the second invocation. We fail to replace Item_in_subselect in prep_on_expr, because prep_on_expr shares the "sub-item" that contains Item_in_subselect with on_expr.
First, we do [successfull] replace in on_expr, which also makes the replace in prep_on_expr.
Second, we attempt to do the replace in prep_on_expr, and that fails.
Launchpad bug id: 878753
Re: Assertion `0' failed in replace_where_subcondition with derived_merge and first execution of prepared statement
Also reproducible without a subquery in the ON clause. Let me know if you require such a testcase.