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Bug#32848: Data type conversion bug in union subselects in MySQL 5.0.38

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There were two problems when inferring the correct field types resulting from
UNION queries.
- If the type is NULL for all corresponding fields in the UNION, the resulting 
  type would be NULL, while the type is BINARY(0) if there is just a single 
  SELECT NULL.
- If one SELECT in the UNION uses a subselect, a temporary table is created
  to represent the subselect, and the result type defaults to a STRING type,
  hiding the fact that the type was unknown(just a NULL value).
Fixed by remembering whenever a field was created from a NULL value and pass
type NULL to the type coercion if that is the case, and creating a string field
as result of UNION only if the type would otherwise be NULL.


mysql-test/r/union.result:
  Bug#32848: Test result
mysql-test/t/union.test:
  Bug#32848: Test case
sql/field.cc:
  Bug#32848: Initialization of new field
sql/field.h:
  Bug#32848: New member to record when a field was created from a NULL value.
sql/item.cc:
  Bug#32848: 
  A field created from a NULL value will submit NULL as type to the 
  type coercion procedure.
  If Item_type_holder has not inferred the correct type after processing all
  SELECTs in a UNION, a string field is created.
sql/sql_select.cc:
  Bug#32848: Recording when a field is created from a NULL value.
This commit is contained in:
unknown
2007-12-11 20:15:03 +01:00
parent 62a7e160bc
commit 94f75ffcce
6 changed files with 66 additions and 1 deletions
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2
sql/sql_select.cc
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@@ -8974,6 +8974,8 @@ 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;
}