Fix bug lp:827416

Analysis:
Constant table optimization of the outer query finds that
the right side of the equality is a constant that can
be used for an eq_ref access to fetch one row from t1,
and substitute t1 with a constant. Thus constant optimization
triggers evaluation of the subquery during the optimize
phase of the outer query.

The innermost subquery requires a plan with a temporary
table because with InnoDB tables the exact count of rows
is not known, and the empty tables cannot be optimzied
way. JOIN::exec for the innermost subquery substitutes
the subquery tables with a temporary table.

When EXPLAIN gets to print the tables in the innermost
subquery, EXPLAIN needs to print the name of each table
through the corresponding TABLE_LIST object. However,
the temporary table created during execution doesn't
have a corresponding TABLE_LIST, so we get a null
pointer exception.

Solution:
The solution is to forbid using expensive constant
expressions for eq_ref access for contant table
optimization. Notice that eq_ref with a subquery
providing the value is still possible during regular
execution.

12 files changed, 125 insertions, 34 deletions

diff --git a/mysql-test/r/group_min_max.result b/mysql-test/r/group_min_max.result
index 6850d7c1993..dc078687fd3 100644
--- a/mysql-test/r/group_min_max.result
+++ b/mysql-test/r/group_min_max.result
@@ -2900,7 +2900,7 @@ NULL
 EXPLAIN
 SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+x	x	x	x	x	x	x	x	x	Using where; Using index
 x	x	x	x	x	x	x	x	x	Using where; Using index
 SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
 MIN( a )
diff --git a/mysql-test/r/subselect.result b/mysql-test/r/subselect.result
index f5d6fea60fc..4411d5ffda2 100644
--- a/mysql-test/r/subselect.result
+++ b/mysql-test/r/subselect.result
@@ -367,12 +367,12 @@ INSERT INTO t8 (pseudo,email) VALUES ('joce1','test1');
 INSERT INTO t8 (pseudo,email) VALUES ('2joce1','2test1');
 EXPLAIN EXTENDED SELECT pseudo,(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce')) FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
+1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using where; Using index
 4	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
-2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
+2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index condition
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
+Note	1003	select `test`.`t8`.`pseudo` AS `pseudo`,(select `test`.`t8`.`email` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -543,6 +543,12 @@ SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT
 numreponse	(SELECT numeropost FROM t1 HAVING numreponse=1)
 INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
+2	SUBQUERY	t1	ref	PRIMARY	PRIMARY	3	const	2	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select 1 from `test`.`t1` where (`test`.`t1`.`numeropost` = 1))))
+SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
 ERROR 21000: Subquery returns more than 1 row
 EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
@@ -551,10 +557,10 @@ Warnings:
 Note	1003	select max(`test`.`t1`.`numreponse`) AS `MAX(numreponse)` from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`)
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select 3 AS `numreponse` from `test`.`t1` where ((3 = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);
diff --git a/mysql-test/r/subselect_innodb.result b/mysql-test/r/subselect_innodb.result
index bf97b9fc4eb..b311fa24eee 100644
--- a/mysql-test/r/subselect_innodb.result
+++ b/mysql-test/r/subselect_innodb.result
@@ -247,4 +247,28 @@ x
 NULL
 drop procedure p1;
 drop tables t1,t2,t3;
+#
+# LP BUG#827416: Crash in select_describe() on EXPLAIN with DISTINCT in nested subqueries
+#
+CREATE TABLE t3 ( b int) ENGINE=InnoDB;
+CREATE TABLE t2 ( c int) ENGINE=InnoDB;
+CREATE TABLE t1 ( a int NOT NULL , PRIMARY KEY (a)) ENGINE=InnoDB;
+EXPLAIN SELECT *
+FROM t1
+WHERE t1.a = (
+SELECT SUM( c )
+FROM t2
+WHERE (SELECT DISTINCT b FROM t3) > 0);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	const	PRIMARY	PRIMARY	4	const	1	Using where; Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	1	
+3	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	1	Using temporary
+SELECT *
+FROM t1
+WHERE t1.a = (
+SELECT SUM( c )
+FROM t2
+WHERE (SELECT DISTINCT b FROM t3) > 0);
+a
+DROP TABLE t1, t2, t3;
 set optimizer_switch=@subselect_innodb_tmp;
diff --git a/mysql-test/r/subselect_no_mat.result b/mysql-test/r/subselect_no_mat.result
index cecc74514c2..dd9e9dc3e0e 100644
--- a/mysql-test/r/subselect_no_mat.result
+++ b/mysql-test/r/subselect_no_mat.result
@@ -372,12 +372,12 @@ INSERT INTO t8 (pseudo,email) VALUES ('joce1','test1');
 INSERT INTO t8 (pseudo,email) VALUES ('2joce1','2test1');
 EXPLAIN EXTENDED SELECT pseudo,(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce')) FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
+1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using where; Using index
 4	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
-2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
+2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index condition
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
+Note	1003	select `test`.`t8`.`pseudo` AS `pseudo`,(select `test`.`t8`.`email` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -548,6 +548,12 @@ SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT
 numreponse	(SELECT numeropost FROM t1 HAVING numreponse=1)
 INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
+2	SUBQUERY	t1	ref	PRIMARY	PRIMARY	3	const	2	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select 1 from `test`.`t1` where (`test`.`t1`.`numeropost` = 1))))
+SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
 ERROR 21000: Subquery returns more than 1 row
 EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
@@ -556,10 +562,10 @@ Warnings:
 Note	1003	select max(`test`.`t1`.`numreponse`) AS `MAX(numreponse)` from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`)
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select 3 AS `numreponse` from `test`.`t1` where ((3 = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);
diff --git a/mysql-test/r/subselect_no_opts.result b/mysql-test/r/subselect_no_opts.result
index e0604485efb..4f1b9f350f8 100644
--- a/mysql-test/r/subselect_no_opts.result
+++ b/mysql-test/r/subselect_no_opts.result
@@ -368,12 +368,12 @@ INSERT INTO t8 (pseudo,email) VALUES ('joce1','test1');
 INSERT INTO t8 (pseudo,email) VALUES ('2joce1','2test1');
 EXPLAIN EXTENDED SELECT pseudo,(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce')) FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
+1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using where; Using index
 4	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
-2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
+2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index condition
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
+Note	1003	select `test`.`t8`.`pseudo` AS `pseudo`,(select `test`.`t8`.`email` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -544,6 +544,12 @@ SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT
 numreponse	(SELECT numeropost FROM t1 HAVING numreponse=1)
 INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
+2	SUBQUERY	t1	ref	PRIMARY	PRIMARY	3	const	2	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select 1 from `test`.`t1` where (`test`.`t1`.`numeropost` = 1))))
+SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
 ERROR 21000: Subquery returns more than 1 row
 EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
@@ -552,10 +558,10 @@ Warnings:
 Note	1003	select max(`test`.`t1`.`numreponse`) AS `MAX(numreponse)` from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`)
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select 3 AS `numreponse` from `test`.`t1` where ((3 = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);
diff --git a/mysql-test/r/subselect_no_semijoin.result b/mysql-test/r/subselect_no_semijoin.result
index 17a4c16531d..d68bbacc7b9 100644
--- a/mysql-test/r/subselect_no_semijoin.result
+++ b/mysql-test/r/subselect_no_semijoin.result
@@ -368,12 +368,12 @@ INSERT INTO t8 (pseudo,email) VALUES ('joce1','test1');
 INSERT INTO t8 (pseudo,email) VALUES ('2joce1','2test1');
 EXPLAIN EXTENDED SELECT pseudo,(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce')) FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
+1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using where; Using index
 4	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
-2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
+2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index condition
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
+Note	1003	select `test`.`t8`.`pseudo` AS `pseudo`,(select `test`.`t8`.`email` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -544,6 +544,12 @@ SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT
 numreponse	(SELECT numeropost FROM t1 HAVING numreponse=1)
 INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
+2	SUBQUERY	t1	ref	PRIMARY	PRIMARY	3	const	2	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select 1 from `test`.`t1` where (`test`.`t1`.`numeropost` = 1))))
+SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
 ERROR 21000: Subquery returns more than 1 row
 EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
@@ -552,10 +558,10 @@ Warnings:
 Note	1003	select max(`test`.`t1`.`numreponse`) AS `MAX(numreponse)` from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`)
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select 3 AS `numreponse` from `test`.`t1` where ((3 = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);
diff --git a/mysql-test/r/subselect_scache.result b/mysql-test/r/subselect_scache.result
index 9405482570b..1dff1ab8921 100644
--- a/mysql-test/r/subselect_scache.result
+++ b/mysql-test/r/subselect_scache.result
@@ -371,12 +371,12 @@ INSERT INTO t8 (pseudo,email) VALUES ('joce1','test1');
 INSERT INTO t8 (pseudo,email) VALUES ('2joce1','2test1');
 EXPLAIN EXTENDED SELECT pseudo,(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce')) FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
+1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using where; Using index
 4	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
-2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
+2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index condition
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
+Note	1003	select `test`.`t8`.`pseudo` AS `pseudo`,(select `test`.`t8`.`email` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -547,6 +547,12 @@ SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT
 numreponse	(SELECT numeropost FROM t1 HAVING numreponse=1)
 INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
+2	SUBQUERY	t1	ref	PRIMARY	PRIMARY	3	const	2	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select 1 from `test`.`t1` where (`test`.`t1`.`numeropost` = 1))))
+SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
 ERROR 21000: Subquery returns more than 1 row
 EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
@@ -555,10 +561,10 @@ Warnings:
 Note	1003	select max(`test`.`t1`.`numreponse`) AS `MAX(numreponse)` from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`)
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select 3 AS `numreponse` from `test`.`t1` where ((3 = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);
diff --git a/mysql-test/suite/pbxt/r/subselect.result b/mysql-test/suite/pbxt/r/subselect.result
index b8b63ed5850..6623251baa0 100644
--- a/mysql-test/suite/pbxt/r/subselect.result
+++ b/mysql-test/suite/pbxt/r/subselect.result
@@ -362,12 +362,12 @@ INSERT INTO t8 (pseudo,email) VALUES ('joce1','test1');
 INSERT INTO t8 (pseudo,email) VALUES ('2joce1','2test1');
 EXPLAIN EXTENDED SELECT pseudo,(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce')) FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
+1	PRIMARY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using where; Using index
 4	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
-2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
+2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using where
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
+Note	1003	select `test`.`t8`.`pseudo` AS `pseudo`,(select `test`.`t8`.`email` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where (`test`.`t8`.`pseudo` = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -535,6 +535,12 @@ SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT
 numreponse	(SELECT numeropost FROM t1 HAVING numreponse=1)
 INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
+2	SUBQUERY	t1	ref	PRIMARY	PRIMARY	3	const	2	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select 1 from `test`.`t1` where (`test`.`t1`.`numeropost` = 1))))
+SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
 ERROR 21000: Subquery returns more than 1 row
 EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
@@ -543,10 +549,10 @@ Warnings:
 Note	1003	select max(`test`.`t1`.`numreponse`) AS `MAX(numreponse)` from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`)
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
+1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using where; Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select 3 AS `numreponse` from `test`.`t1` where ((3 = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
+Note	1003	select `test`.`t1`.`numreponse` AS `numreponse` from `test`.`t1` where ((`test`.`t1`.`numeropost` = 1) and (`test`.`t1`.`numreponse` = (select max(`test`.`t1`.`numreponse`) from `test`.`t1` where multiple equal(1, `test`.`t1`.`numeropost`))))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);
diff --git a/mysql-test/suite/pbxt/t/subselect.test b/mysql-test/suite/pbxt/t/subselect.test
index 3f4d6a9a870..3b7348ce844 100644
--- a/mysql-test/suite/pbxt/t/subselect.test
+++ b/mysql-test/suite/pbxt/t/subselect.test
@@ -278,8 +278,9 @@ SELECT (SELECT numeropost FROM t1 HAVING numreponse=a),numreponse FROM (SELECT *
 SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=a) FROM (SELECT * FROM t1) as a;
 SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT * FROM t1) as a;
 INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
--- error 1242
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
+-- error 1242
+SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
 EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 drop table t1;
diff --git a/mysql-test/t/subselect.test b/mysql-test/t/subselect.test
index 6c460af6ae5..d460eb57667 100644
--- a/mysql-test/t/subselect.test
+++ b/mysql-test/t/subselect.test
@@ -292,8 +292,9 @@ SELECT (SELECT numeropost FROM t1 HAVING numreponse=a),numreponse FROM (SELECT *
 SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=a) FROM (SELECT * FROM t1) as a;
 SELECT numreponse, (SELECT numeropost FROM t1 HAVING numreponse=1) FROM (SELECT * FROM t1) as a;
 INSERT INTO t1 (numeropost,numreponse,pseudo) VALUES (1,1,'joce'),(1,2,'joce'),(1,3,'test');
--- error ER_SUBQUERY_NO_1_ROW
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
+-- error ER_SUBQUERY_NO_1_ROW
+SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT 1 FROM t1 WHERE numeropost='1');
 EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 drop table t1;
diff --git a/mysql-test/t/subselect_innodb.test b/mysql-test/t/subselect_innodb.test
index da7524c1427..e108aecfd36 100644
--- a/mysql-test/t/subselect_innodb.test
+++ b/mysql-test/t/subselect_innodb.test
@@ -241,5 +241,27 @@ call p1();
 drop procedure p1;
 drop tables t1,t2,t3;
 
-set optimizer_switch=@subselect_innodb_tmp;
+--echo #
+--echo # LP BUG#827416: Crash in select_describe() on EXPLAIN with DISTINCT in nested subqueries
+--echo #
+
+CREATE TABLE t3 ( b int) ENGINE=InnoDB;
+CREATE TABLE t2 ( c int) ENGINE=InnoDB;
+CREATE TABLE t1 ( a int NOT NULL , PRIMARY KEY (a)) ENGINE=InnoDB;
+
+EXPLAIN SELECT *
+FROM t1
+WHERE t1.a = (
+        SELECT SUM( c )
+        FROM t2
+        WHERE (SELECT DISTINCT b FROM t3) > 0);
+SELECT *
+FROM t1
+WHERE t1.a = (
+        SELECT SUM( c )
+        FROM t2
+        WHERE (SELECT DISTINCT b FROM t3) > 0);
 
+DROP TABLE t1, t2, t3;
+
+set optimizer_switch=@subselect_innodb_tmp;
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 6d2c7400d3d..54c1215164e 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -2993,6 +2993,7 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
   uint i,table_count,const_count,key;
   table_map found_const_table_map, all_table_map, found_ref, refs;
   key_map const_ref, eq_part;
+  bool has_expensive_keyparts;
   TABLE **table_vector;
   JOIN_TAB *stat,*stat_end,*s,**stat_ref;
   KEYUSE *keyuse,*start_keyuse;
@@ -3314,12 +3315,17 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
 	  refs=0;
           const_ref.clear_all();
 	  eq_part.clear_all();
+          has_expensive_keyparts= false;
 	  do
 	  {
 	    if (keyuse->val->type() != Item::NULL_ITEM && !keyuse->optimize)
 	    {
 	      if (!((~found_const_table_map) & keyuse->used_tables))
+              {
 		const_ref.set_bit(keyuse->keypart);
+                if (keyuse->val->is_expensive())
+                  has_expensive_keyparts= true;
+              }
 	      else
 		refs|=keyuse->used_tables;
 	      eq_part.set_bit(keyuse->keypart);
@@ -3341,6 +3347,7 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
             if (table->key_info[key].flags & HA_NOSAME)
             {
 	      if (const_ref == eq_part &&
+                  !has_expensive_keyparts &&
                   !((outer_join & table->map) &&
                     (*s->on_expr_ref)->is_expensive()))
 	      {					// Found everything for ref.