Merge mhansson@bk-internal:/home/bk/mysql-5.1-opt

into  linux-st28.site:/home/martin/mysql/src/bug32848/my51-bug32848

mysql-test/r/union.result

@@ -1496,4 +1496,28 @@ UNION
 SELECT 1,1;
 ERROR HY000: Incorrect usage of UNION and ORDER BY
 DROP TABLE t1,t2;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1), (2), (3);
+CREATE TABLE t2 SELECT * FROM (SELECT NULL) a UNION SELECT a FROM t1;
+DESC t2;
+Field	Type	Null	Key	Default	Extra
+NULL	int(11)	YES		NULL	
+CREATE TABLE t3 SELECT a FROM t1 UNION SELECT * FROM (SELECT NULL) a;
+DESC t3;
+Field	Type	Null	Key	Default	Extra
+a	int(11)	YES		NULL	
+CREATE TABLE t4 SELECT NULL;
+DESC t4;
+Field	Type	Null	Key	Default	Extra
+NULL	binary(0)	YES		NULL	
+CREATE TABLE t5 SELECT NULL UNION SELECT NULL;
+DESC t5;
+Field	Type	Null	Key	Default	Extra
+NULL	binary(0)	YES		NULL	
+CREATE TABLE t6 
+SELECT * FROM (SELECT * FROM (SELECT NULL)a) b UNION SELECT a FROM t1;
+DESC t6;
+Field	Type	Null	Key	Default	Extra
+NULL	int(11)	YES		NULL	
+DROP TABLE t1, t2, t3, t4, t5, t6;
 End of 5.0 tests

mysql-test/t/union.test

@@ -966,4 +966,26 @@ SELECT 1,1;
 
 DROP TABLE t1,t2;
 
+# Bug#32848: Data type conversion bug in union subselects in MySQL 5.0.38
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1), (2), (3);
+
+CREATE TABLE t2 SELECT * FROM (SELECT NULL) a UNION SELECT a FROM t1;
+DESC t2;
+
+CREATE TABLE t3 SELECT a FROM t1 UNION SELECT * FROM (SELECT NULL) a;
+DESC t3;
+
+CREATE TABLE t4 SELECT NULL;
+DESC t4;
+
+CREATE TABLE t5 SELECT NULL UNION SELECT NULL;
+DESC t5;
+
+CREATE TABLE t6 
+SELECT * FROM (SELECT * FROM (SELECT NULL)a) b UNION SELECT a FROM t1;
+DESC t6;
+
+DROP TABLE t1, t2, t3, t4, t5, t6;
 --echo End of 5.0 tests

sql/field.cc

@@ -1307,7 +1307,8 @@ Field::Field(uchar *ptr_arg,uint32 length_arg,uchar *null_ptr_arg,
    field_name(field_name_arg),
    key_start(0), part_of_key(0), part_of_key_not_clustered(0),
    part_of_sortkey(0), unireg_check(unireg_check_arg),
-   field_length(length_arg), null_bit(null_bit_arg)
+   field_length(length_arg), null_bit(null_bit_arg), 
+   is_created_from_null_item(FALSE)
 {
   flags=null_ptr ? 0: NOT_NULL_FLAG;
   comment.str= (char*) "";

sql/field.h

@@ -90,6 +90,16 @@ class Field
   uint32	flags;
   uint16        field_index;            // field number in fields array
   uchar		null_bit;		// Bit used to test null bit
+  /**
+     If true, this field was created in create_tmp_field_from_item from a NULL
+     value. This means that the type of the field is just a guess, and the type
+     may be freely coerced to another type.
+
+     @see create_tmp_field_from_item
+     @see Item_type_holder::get_real_type
+
+   */
+  bool is_created_from_null_item;
 
   Field(uchar *ptr_arg,uint32 length_arg,uchar *null_ptr_arg,
         uchar null_bit_arg, utype unireg_check_arg,

sql/item.cc

@@ -6707,6 +6707,8 @@ enum_field_types Item_type_holder::get_real_type(Item *item)
     */
     Field *field= ((Item_field *) item)->field;
     enum_field_types type= field->real_type();
+    if (field->is_created_from_null_item)
+      return MYSQL_TYPE_NULL;
     /* work around about varchar type field detection */
     if (type == MYSQL_TYPE_STRING && field->type() == MYSQL_TYPE_VAR_STRING)
       return MYSQL_TYPE_VAR_STRING;
@@ -6965,6 +6967,8 @@ Field *Item_type_holder::make_field_by_type(TABLE *table)
     if (field)
       field->init(table);
     return field;
+  case MYSQL_TYPE_NULL:
+    return make_string_field(table);
   default:
     break;
   }

sql/sql_select.cc

@@ -9277,6 +9277,8 @@ static Field *create_tmp_field_from_item(THD *thd, Item *item, TABLE *table,
     *((*copy_func)++) = item;			// Save for copy_funcs
   if (modify_item)
     item->set_result_field(new_field);
+  if (item->type() == Item::NULL_ITEM)
+    new_field->is_created_from_null_item= TRUE;
   return new_field;
 }