Fixed LP bug #803410.

Due to this bug in the function generate_derived_keys_for_table some
key definitions to access materialized derived tables or materialized
views were constructed with invalid info for their key parts.
This could make the server crash when it optimized queries using 
materialized derived tables or materialized views. 

mysql-test/r/derived_view.result

@@ -703,3 +703,25 @@ a
 NULL
 DROP VIEW v1;
 DROP TABLE t1,t2,t3;
+#
+# LP bug #803410: materialized view/dt accessed by two-component key                       
+#                 
+CREATE TABLE t1 (a varchar(1));
+INSERT INTO t1 VALUES ('c');
+CREATE TABLE t2 (a varchar(1) , KEY (a)) ;
+INSERT INTO t2 VALUES ('c'), (NULL), ('r');
+CREATE TABLE t3 (a varchar(1), b varchar(1));
+INSERT INTO t3 VALUES ('e', 'c'), ('c', 'c'), ('c', 'r');
+CREATE VIEW v1 AS SELECT a, MIN(b) AS b FROM t3 GROUP BY a;
+EXPLAIN
+SELECT * FROM t1, t2, v1 WHERE t2.a=t1.a AND t2.a=v1.a AND t2.a=v1.b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	t2	ref	a	a	4	const	1	Using index
+1	PRIMARY	<derived2>	ref	key1	key1	10	test.t1.a,test.t1.a	2	Using where
+2	DERIVED	t3	ALL	NULL	NULL	NULL	NULL	3	Using temporary; Using filesort
+SELECT * FROM t1, t2, v1 WHERE t2.a=t1.a AND t2.a=v1.a AND t2.a=v1.b;
+a	a	a	b
+c	c	c	c
+DROP VIEW v1;
+DROP TABLE t1,t2,t3;

mysql-test/t/derived_view.test

@@ -322,3 +322,24 @@ SELECT t.a FROM t1 LEFT JOIN
 DROP VIEW v1;
 DROP TABLE t1,t2,t3;
 
+--echo #
+--echo # LP bug #803410: materialized view/dt accessed by two-component key                       
+--echo #                 
+
+CREATE TABLE t1 (a varchar(1));
+INSERT INTO t1 VALUES ('c');
+
+CREATE TABLE t2 (a varchar(1) , KEY (a)) ;
+INSERT INTO t2 VALUES ('c'), (NULL), ('r');
+
+CREATE TABLE t3 (a varchar(1), b varchar(1));
+INSERT INTO t3 VALUES ('e', 'c'), ('c', 'c'), ('c', 'r');
+
+CREATE VIEW v1 AS SELECT a, MIN(b) AS b FROM t3 GROUP BY a;
+
+EXPLAIN
+SELECT * FROM t1, t2, v1 WHERE t2.a=t1.a AND t2.a=v1.a AND t2.a=v1.b;
+SELECT * FROM t1, t2, v1 WHERE t2.a=t1.a AND t2.a=v1.a AND t2.a=v1.b;
+
+DROP VIEW v1;
+DROP TABLE t1,t2,t3;

sql/sql_select.cc

@@ -8293,6 +8293,7 @@ bool generate_derived_keys_for_table(KEYUSE *keyuse, uint count, uint keys)
       first_keyuse= keyuse;
       keyno++;
       parts= 0;
+      prev_part= (uint) (-1);
     }
     else if (keyuse->keypart != prev_part)
     {