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Fixed bug #28728: a crash when executing EXPLAIN EXTENDED for a query

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using a derived table over a grouping subselect.

This crash happens only when materialization of the derived tables 
requires creation of auxiliary temporary table, for example when
a grouping operation is carried out with usage of a temporary table.

The crash happened because EXPLAIN EXTENDED when printing the query
expression made an attempt to use the objects created in the mem_root
of the temporary table which has been already freed by the moment
when printing is called.

This bug appeared after the method Item_field::print() had been 
introduced.    


mysql-test/r/subselect.result:
  Added a test case for bug #28728.
mysql-test/t/subselect.test:
  Added a test case for bug #28728.
sql/sql_select.cc:
  Fixed bug #28728: a crash when executing EXPLAIN EXTENDED for a query
  using a derived table over a grouping subselect.
  The crash happened because EXPLAIN EXTENDED when printing the query
  expression made an attempt to use the objects created in the mem_root
  of the temporary table which has been already freed by the moment
  when printing is accomplished.
  The fix in JOIN::exec() ensures using existing objects when printing 
  subselects for a derived tables by EXPLAIN EXTENDED.
This commit is contained in:
unknown
2007-06-02 11:44:16 -07:00
parent 0ec40a459e
commit 8c4ff24b56
3 changed files with 35 additions and 0 deletions
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11
sql/sql_select.cc
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@@ -2075,6 +2075,17 @@ JOIN::exec()
thd->examined_row_count+= curr_join->examined_rows;
DBUG_PRINT("counts", ("thd->examined_row_count: %lu",
(ulong) thd->examined_row_count));
/*
With EXPLAIN EXTENDED we have to restore original ref_array
for a derived table which is always materialized.
Otherwise we would not be able to print the query correctly.
*/
if (items0 &&
(thd->lex->describe & DESCRIBE_EXTENDED) &&
select_lex->linkage == DERIVED_TABLE_TYPE)
set_items_ref_array(items0);
DBUG_VOID_RETURN;
}