6 files changed, 34 insertions, 5 deletions
diff --git a/mysql-test/r/partition_column.result b/mysql-test/r/partition_column.result
index 8c7d5b4ff77..9d46c6e0805 100644
--- a/mysql-test/r/partition_column.result
+++ b/mysql-test/r/partition_column.result
@@ -110,7 +110,7 @@ a
 NULL
 explain partitions select * from t1 where a is null;
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	p0	ALL	NULL	NULL	NULL	NULL	10	Using where
+1	SIMPLE	t1	p0	ALL	NULL	NULL	NULL	NULL	2	Using where
 select * from t1 where a <= 1;
 a
 1
diff --git a/mysql-test/r/partition_pruning.result b/mysql-test/r/partition_pruning.result
index f59316e9ce8..d7790cd8075 100644
--- a/mysql-test/r/partition_pruning.result
+++ b/mysql-test/r/partition_pruning.result
@@ -1601,10 +1601,9 @@ 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,
diff --git a/mysql-test/r/range.result b/mysql-test/r/range.result
index c98a7696ea6..0d44e79b39a 100644
--- a/mysql-test/r/range.result
+++ b/mysql-test/r/range.result
@@ -1398,3 +1398,12 @@ a < 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	range	a	a	5	NULL	8	Using where; Using index
 DROP TABLE t1, t2, t3;
+#
+# 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;
+End of 5.1 tests
diff --git a/mysql-test/r/subselect.result b/mysql-test/r/subselect.result
index fc0a933b732..e8e8e1f78fb 100644
--- a/mysql-test/r/subselect.result
+++ b/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;
diff --git a/mysql-test/t/range.test b/mysql-test/t/range.test
index dc119b6a77e..f0fa99f3d95 100644
--- a/mysql-test/t/range.test
+++ b/mysql-test/t/range.test
@@ -1171,3 +1171,14 @@ a < 5 OR
 a < 10;
 
 DROP TABLE t1, t2, t3;
+
+--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;
+
+--echo End of 5.1 tests
diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index ce86fa535fe..61122b9892d 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -6067,6 +6067,17 @@ 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;