BUG#20492: Subsequent calls to stored procedure yield incorrect result

           if join is used

For procedures with selects that use complicated joins with ON expression
re-execution could erroneously ignore this ON expression, giving
incorrect result.

The problem was that optimized ON expression wasn't saved for
re-execution.  The solution is to properly save it.

mysql-test/r/sp.result

@@ -5394,4 +5394,30 @@ Procedure	sql_mode	Create Procedure
 bug21416		CREATE DEFINER=`root`@`localhost` PROCEDURE `bug21416`()
 show create procedure bug21416
 drop procedure bug21416|
+DROP PROCEDURE IF EXISTS p1|
+DROP VIEW IF EXISTS v1, v2|
+DROP TABLE IF EXISTS t3, t4|
+CREATE TABLE t3 (t3_id INT)|
+INSERT INTO t3 VALUES (0)|
+INSERT INTO t3 VALUES (1)|
+CREATE TABLE t4 (t4_id INT)|
+INSERT INTO t4 VALUES (2)|
+CREATE VIEW v1 AS
+SELECT t3.t3_id, t4.t4_id
+FROM t3 JOIN t4 ON t3.t3_id = 0|
+CREATE VIEW v2 AS
+SELECT t3.t3_id AS t3_id_1, v1.t3_id AS t3_id_2, v1.t4_id
+FROM t3 LEFT JOIN v1 ON t3.t3_id = 0|
+CREATE PROCEDURE p1() SELECT * FROM v2|
+CALL p1()|
+t3_id_1	t3_id_2	t4_id
+0	0	2
+1	NULL	NULL
+CALL p1()|
+t3_id_1	t3_id_2	t4_id
+0	0	2
+1	NULL	NULL
+DROP PROCEDURE p1|
+DROP VIEW v1, v2|
+DROP TABLE t3, t4|
 drop table t1,t2;

mysql-test/t/sp.test

@@ -6322,6 +6322,47 @@ create procedure bug21416() show create procedure bug21416|
 call bug21416()|
 drop procedure bug21416|
 
+
+#
+# BUG#20492: Subsequent calls to stored procedure yeild incorrect
+# result if join is used 
+#
+# Optimized ON expression in join wasn't properly saved for reuse.
+#
+--disable_warnings
+DROP PROCEDURE IF EXISTS p1|
+DROP VIEW IF EXISTS v1, v2|
+DROP TABLE IF EXISTS t3, t4|
+--enable_warnings
+
+CREATE TABLE t3 (t3_id INT)|
+
+INSERT INTO t3 VALUES (0)|
+INSERT INTO t3 VALUES (1)|
+
+CREATE TABLE t4 (t4_id INT)|
+
+INSERT INTO t4 VALUES (2)|
+
+CREATE VIEW v1 AS
+SELECT t3.t3_id, t4.t4_id
+FROM t3 JOIN t4 ON t3.t3_id = 0|
+
+CREATE VIEW v2 AS
+SELECT t3.t3_id AS t3_id_1, v1.t3_id AS t3_id_2, v1.t4_id
+FROM t3 LEFT JOIN v1 ON t3.t3_id = 0|
+
+CREATE PROCEDURE p1() SELECT * FROM v2|
+
+# Results should not differ.
+CALL p1()|
+CALL p1()|
+
+DROP PROCEDURE p1|
+DROP VIEW v1, v2|
+DROP TABLE t3, t4|
+
+
 #
 # BUG#NNNN: New bug synopsis
 #

sql/sql_select.cc

@@ -7427,9 +7427,14 @@ simplify_joins(JOIN *join, List<TABLE_LIST> *join_list, COND *conds, bool top)
 	*/ 
         expr= simplify_joins(join, &nested_join->join_list,
                              expr, FALSE);
-        table->on_expr= expr;
-        if (!table->prep_on_expr)
+
+        if (!table->prep_on_expr || expr != table->on_expr)
+        {
+          DBUG_ASSERT(expr);
+
+          table->on_expr= expr;
           table->prep_on_expr= expr->copy_andor_structure(join->thd);
+        }
       }
       nested_join->used_tables= (table_map) 0;
       nested_join->not_null_tables=(table_map) 0;
@@ -7439,7 +7444,7 @@ simplify_joins(JOIN *join, List<TABLE_LIST> *join_list, COND *conds, bool top)
     }
     else
     {
-      if (!(table->prep_on_expr))
+      if (!table->prep_on_expr)
         table->prep_on_expr= table->on_expr;
       used_tables= table->table->map;
       if (conds)