Merge mhansson@bk-internal:/home/bk/mysql-5.0-opt

into  linux-st28.site:/home/martin/mysql/src/bug32848/my50-bug32848


sql/field.cc:
  Auto merged
sql/field.h:
  Auto merged
sql/item.cc:
  Auto merged
sql/sql_select.cc:
  Auto merged
mysql-test/r/union.result:
  Bug#32848: Manual merge
mysql-test/t/union.test:
  Bug#32848: Manual merge

4 files changed, 18 insertions, 1 deletions

diff --git a/sql/field.cc b/sql/field.cc
index 3f00b6750bc..b1cc3701f3d 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -1304,7 +1304,8 @@ Field::Field(char *ptr_arg,uint32 length_arg,uchar *null_ptr_arg,
    field_name(field_name_arg),
    query_id(0), key_start(0), part_of_key(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*) "";
diff --git a/sql/field.h b/sql/field.h
index 05c22092e53..e5c473ed556 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -89,6 +89,16 @@ public:
   uint          field_index;            // field number in fields array
   uint16	flags;
   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(char *ptr_arg,uint32 length_arg,uchar *null_ptr_arg,uchar null_bit_arg,
 	utype unireg_check_arg, const char *field_name_arg,
diff --git a/sql/item.cc b/sql/item.cc
index 975b517284f..2d49c7b6d60 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -6608,6 +6608,8 @@ 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;
@@ -6859,6 +6861,8 @@ Field *Item_type_holder::make_field_by_type(TABLE *table)
                          Field::NONE, name,
                          table, get_set_pack_length(enum_set_typelib->count),
                          enum_set_typelib, collation.collation);
+  case MYSQL_TYPE_NULL:
+    return make_string_field(table);
   default:
     break;
   }
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index d6cb072ce9b..47a4097964a 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -9041,6 +9041,8 @@ 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() == MYSQL_TYPE_NULL)
+    new_field->is_created_from_null_item= TRUE;
   return new_field;
 }