Backport into build-200911241145-5.1.40sp1

> ------------------------------------------------------------
> revno: 3181
> revision-id: alexey.kopytov@sun.com-20091016201951-fsht0wm8xn8vkzsx
> parent: joerg@mysql.com-20091016164025-kb4sbrggq5o7zufc
> committer: Alexey Kopytov <Alexey.Kopytov@Sun.com>
> branch nick: mysql-5.1-bugteam
> timestamp: Sat 2009-10-17 00:19:51 +0400
> message:
>   Bug #47123: Endless 100% CPU loop with STRAIGHT_JOIN 
>    
>   The problem was in incorrect handling of predicates involving 
>   NULL as a constant value by the range optimizer. 
>    
>   For example, when creating a SEL_ARG node from a condition of 
>   the form "field < const" (which would normally result in the 
>   "NULL < field < const" SEL_ARG),  the special case when "const" 
>   is NULL was not taken into account, so "NULL < field < NULL" 
>   was produced for the "field < NULL" condition. 
>    
>   As a result, SEL_ARG structures of this form could not be 
>   further optimized which in turn could lead to incorrectly 
>   constructed SEL_ARG trees. In particular, code assuming SEL_ARG 
>   structures to always form a sequence of ordered disjoint 
>   intervals could enter an infinite loop under some 
>   circumstances. 
>    
>   Fixed by changing get_mm_leaf() so that for any sargable 
>   predicate except "<=>" involving NULL as a constant, "empty" 
>   SEL_ARG is returned, since such a predicate is always false. 

mysql-test/r/partition_pruning.result

@@ -1272,10 +1272,9 @@ INSERT INTO t1 VALUES (1, '2009-01-01'), (2, NULL);
 # test with an invalid date, which lead to item->null_value is set.
 EXPLAIN PARTITIONS SELECT * FROM t1 WHERE b < CAST('2009-04-99' AS DATETIME);
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	p20090401	ALL	NULL	NULL	NULL	NULL	2	Using where
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 Warnings:
 Warning	1292	Incorrect datetime value: '2009-04-99'
-Warning	1292	Incorrect datetime value: '2009-04-99'
 DROP TABLE t1;
 CREATE TABLE t1
 (a INT NOT NULL AUTO_INCREMENT,

mysql-test/r/range.result

@@ -1216,6 +1216,14 @@ select 'In following EXPLAIN the access method should be ref, #rows~=500 (and no
 Z
 In following EXPLAIN the access method should be ref, #rows~=500 (and not 2)
 explain select * from t2 where a=1000 and b<11;
+#
+# Bug #47123: Endless 100% CPU loop with STRAIGHT_JOIN
+#
+CREATE TABLE t1(a INT, KEY(a));
+INSERT INTO t1 VALUES (1), (NULL);
+SELECT * FROM t1 WHERE a <> NULL and (a <> NULL or a <= NULL);
+a
+DROP TABLE t1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t2	ref	a	a	5	const	502	Using where
 drop table t1, t2;

mysql-test/r/subselect.result

@@ -4403,8 +4403,7 @@ FROM t1
 WHERE a = 230;
 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
-2	DEPENDENT SUBQUERY	st1	index	NULL	a	5	NULL	2	Using index
-2	DEPENDENT SUBQUERY	st2	index	b	b	5	NULL	2	Using where; Using index; Using join buffer
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 SELECT MAX(b), (SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
 FROM t1 
 WHERE a = 230;

mysql-test/t/range.test

@@ -1043,6 +1043,15 @@ alter table t2 add index (a,b);
 
 select 'In following EXPLAIN the access method should be ref, #rows~=500 (and not 2)' Z;
 explain select * from t2 where a=1000 and b<11;
+--echo #
+--echo # Bug #47123: Endless 100% CPU loop with STRAIGHT_JOIN
+--echo #
+
+CREATE TABLE t1(a INT, KEY(a));
+INSERT INTO t1 VALUES (1), (NULL);
+SELECT * FROM t1 WHERE a <> NULL and (a <> NULL or a <= NULL);
+DROP TABLE t1;
+
 
 drop table t1, t2;
 

sql/opt_range.cc

@@ -5911,6 +5911,17 @@ get_mm_leaf(RANGE_OPT_PARAM *param, COND *conf_func, Field *field,
     goto end;
   }
   field->table->in_use->variables.sql_mode= orig_sql_mode;
+
+  /*
+    Any sargable predicate except "<=>" involving NULL as a constant is always
+    FALSE
+  */
+  if (type != Item_func::EQUAL_FUNC && field->is_real_null())
+  {
+    tree= &null_element;
+    goto end;
+  }
+  
   str= (uchar*) alloc_root(alloc, key_part->store_length+1);
   if (!str)
     goto end;