Fixed LP bug #798576.

If a view/derived table is non-mergeable then the definition of the tmp table
to store the rows for it is created at the prepare stage. In this case if the
view definition uses outer joins and a view column belongs to an inner table
of one of them then the column should be considered as nullable independently
on nullability of the underlying column. If the underlying column happens to be
defined as non-nullable then the function create_tmp_field_from_item rather 
than the function create_tmp_field_from_field should be employed to create
the definition of the interesting column in the tmp table.
 

mysql-test/r/view.result

@@ -4207,3 +4207,25 @@ Warnings:
 Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a` from `test`.`t1` left join `test`.`t2` on((`test`.`t2`.`a` = `test`.`t1`.`a`)) where ((`test`.`t1`.`b` = 1) or ((`test`.`t1`.`a` = 'a') and (length(`test`.`t1`.`a`) >= `test`.`t1`.`b`)))
 DROP VIEW v1;
 DROP TABLE t1,t2;
+#
+# Bug#798576: abort on a GROUP BY query over a view with left join 
+#             that can be converted to inner join
+#
+CREATE TABLE t1 (a int NOT NULL , b int NOT NULL) ;
+INSERT INTO t1 VALUES (214,0), (6,6), (6,0), (7,0);
+CREATE TABLE t2 (b int) ;
+INSERT INTO t2 VALUES (88), (78), (6);
+CREATE ALGORITHM=MERGE VIEW v1 AS 
+SELECT t1.a, t2.b FROM (t2 LEFT JOIN t1 ON t2.b > t1.a) WHERE t1.b <= 0;
+SELECT * FROM v1;
+a	b
+6	88
+6	78
+7	88
+7	78
+SELECT a, MIN(b) FROM v1 GROUP BY a;
+a	MIN(b)
+6	78
+7	78
+DROP VIEW v1;
+DROP TABLE t1,t2;

mysql-test/t/view.test

@@ -4155,3 +4155,24 @@ SELECT * FROM v1 LEFT JOIN t2 ON t2.a = v1.a
 
 DROP VIEW v1;
 DROP TABLE t1,t2;
+
+--echo #
+--echo # Bug#798576: abort on a GROUP BY query over a view with left join 
+--echo #             that can be converted to inner join
+--echo #
+
+CREATE TABLE t1 (a int NOT NULL , b int NOT NULL) ;
+INSERT INTO t1 VALUES (214,0), (6,6), (6,0), (7,0);
+
+CREATE TABLE t2 (b int) ;
+INSERT INTO t2 VALUES (88), (78), (6);
+
+CREATE ALGORITHM=MERGE VIEW v1 AS 
+  SELECT t1.a, t2.b FROM (t2 LEFT JOIN t1 ON t2.b > t1.a) WHERE t1.b <= 0;
+
+SELECT * FROM v1;
+SELECT a, MIN(b) FROM v1 GROUP BY a;
+
+DROP VIEW v1;
+DROP TABLE t1,t2;
+

sql/sql_class.cc

@@ -814,6 +814,7 @@ THD::THD()
   memset(&invoker_user, 0, sizeof(invoker_user));
   memset(&invoker_host, 0, sizeof(invoker_host));
   prepare_derived_at_open= FALSE;
+  create_tmp_table_for_derived= FALSE;
 }
 
 

sql/sql_class.h

@@ -1571,6 +1571,12 @@ public:
 
   bool prepare_derived_at_open;
 
+  /* 
+    To signal that the tmp table to be created is created for materialized
+    derived table or a view.
+  */ 
+  bool create_tmp_table_for_derived;
+
 #ifndef MYSQL_CLIENT
   int binlog_setup_trx_data();
 

sql/sql_derived.cc

@@ -659,13 +659,18 @@ bool mysql_derived_prepare(THD *thd, LEX *lex, TABLE_LIST *derived)
     !unit->union_distinct->next_select() (i.e. it is union and last distinct
     SELECT is last SELECT of UNION).
   */
+  thd->create_tmp_table_for_derived= TRUE;
   if (derived->derived_result->create_result_table(thd, &unit->types, FALSE,
                                                 (first_select->options |
                                                  thd->options |
                                                  TMP_TABLE_ALL_COLUMNS),
                                                 derived->alias,
                                                 FALSE, FALSE))
+  { 
+    thd->create_tmp_table_for_derived= FALSE;
     goto exit;
+  }
+  thd->create_tmp_table_for_derived= FALSE;
 
   derived->table= derived->derived_result->table;
   if (derived->is_derived() && derived->is_merged_derived())

sql/sql_select.cc

@@ -12772,8 +12772,9 @@ Field *create_tmp_field(THD *thd, TABLE *table,Item *item, Item::Type type,
       If item have to be able to store NULLs but underlaid field can't do it,
       create_tmp_field_from_field() can't be used for tmp field creation.
     */
-    if (((field->maybe_null && field->in_rollup) ||
-         (orig_item && orig_item->maybe_null)) && /* for outer joined views/dt*/        
+    if (((field->maybe_null && field->in_rollup) ||      
+	(thd->create_tmp_table_for_derived  &&    /* for mat. view/dt */
+	 orig_item && orig_item->maybe_null)) &&         
         !field->field->maybe_null())
     {
       bool save_maybe_null= FALSE;