Fixed LP bug #794909.

The function generate_derived_keys did not take into account the fact
that the last element in the array of keyuses could be just a barrier
element. In some cases it could lead to a crash of the server.

Also fixed a couple of other bugs in generate_derived_keys: the inner 
loop in the body of if this function did not change the cycle variables
properly.

mysql-test/r/derived_view.result

@@ -568,3 +568,24 @@ TODO: Add test with 64 tables mergeable view to test fall back to
 materialization on tables > MAX_TABLES merge
 drop table t1,t2;
 drop view v1,v2,v3,v4,v6,v7;
+#
+#  LP bug #794909: crash when defining possible keys for
+#                  a materialized view/derived_table
+#
+CREATE TABLE t1 (f1 int) ;
+INSERT INTO t1 VALUES (149), (150), (224), (29);
+CREATE TABLE t2 (f1 int, KEY (f1));
+INSERT INTO t2 VALUES (149), (NULL), (224);
+CREATE ALGORITHM=TEMPTABLE VIEW v1 AS SELECT * FROM t1;
+EXPLAIN
+SELECT * FROM v1 JOIN t2 ON v1.f1 = t2.f1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	index	f1	f1	5	NULL	3	Using where; Using index
+1	PRIMARY	<derived2>	ref	key0	key0	5	test.t2.f1	2	
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	4	
+SELECT * FROM v1 JOIN t2 ON v1.f1 = t2.f1;
+f1	f1
+149	149
+224	224
+DROP VIEW v1;
+DROP TABLE t1,t2;

mysql-test/t/derived_view.test

@@ -215,3 +215,23 @@ select * from t1 join (select * from t2 group by f2) tt on t1.f1=tt.f2 join t1 x
 --echo materialization on tables > MAX_TABLES merge
 drop table t1,t2;
 drop view v1,v2,v3,v4,v6,v7;
+
+--echo #
+--echo #  LP bug #794909: crash when defining possible keys for
+--echo #                  a materialized view/derived_table
+--echo #
+
+CREATE TABLE t1 (f1 int) ;
+INSERT INTO t1 VALUES (149), (150), (224), (29);
+
+CREATE TABLE t2 (f1 int, KEY (f1));
+INSERT INTO t2 VALUES (149), (NULL), (224);
+
+CREATE ALGORITHM=TEMPTABLE VIEW v1 AS SELECT * FROM t1;
+
+EXPLAIN
+SELECT * FROM v1 JOIN t2 ON v1.f1 = t2.f1;
+SELECT * FROM v1 JOIN t2 ON v1.f1 = t2.f1;
+
+DROP VIEW v1;
+DROP TABLE t1,t2;

sql/sql_select.cc

@@ -8328,6 +8328,8 @@ bool generate_derived_keys(DYNAMIC_ARRAY *keyuse_array)
   TABLE *prev_table= 0;
   for (uint i= 0; i < elements; i++, keyuse++)
   {
+    if (!keyuse->table)
+      break;
     KEYUSE *first_table_keyuse= NULL;
     table_map last_used_tables= 0;
     uint count= 0;
@@ -8353,11 +8355,13 @@ bool generate_derived_keys(DYNAMIC_ARRAY *keyuse_array)
       }
       count++;
       keyuse++;
-      if (keyuse->table != prev_table &&
-          generate_derived_keys_for_table(first_table_keyuse, count, ++keys))
-        return TRUE;
-      if (++i == elements)
-        break;
+      if (keyuse->table != prev_table)
+      {
+        if (generate_derived_keys_for_table(first_table_keyuse, count, ++keys))
+          return TRUE;
+        keyuse--;
+	derived= NULL;
+      }
     }
   }
   return FALSE;