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MDEV-19179 Regression: SELECT ... UNION ... with inconsistent column names fails

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A bogus error message was issued when a condition was pushed into a
materialized derived table or view specified as union of selects with
aggregation when the corresponding columns of the selects had different
names. This happened because the expression pushed into having clauses of
the selects was adjusted for the names of the first select of the union.
The easiest solution was to rename the columns of the other selects to be
name compatible with the columns of the first select.

Approved by Oleksandr Byelkin <sanja@mariadb.com>
This commit is contained in:
Igor Babaev
2020-11-18 13:21:19 -08:00
parent bbbab8215f
commit 1248c654c4
4 changed files with 95 additions and 2 deletions
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22
sql/sql_derived.cc
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@@ -1199,7 +1199,8 @@ bool pushdown_cond_for_derived(THD *thd, Item *cond, TABLE_LIST *derived)
DBUG_RETURN(false);
st_select_lex_unit *unit= derived->get_unit();
st_select_lex *sl= unit->first_select();
st_select_lex *first_sl= unit->first_select();
st_select_lex *sl= first_sl;
if (derived->prohibit_cond_pushdown)
DBUG_RETURN(false);
@@ -1311,7 +1312,24 @@ bool pushdown_cond_for_derived(THD *thd, Item *cond, TABLE_LIST *derived)
if (!extracted_cond_copy)
continue;
}
/*
Rename the columns of all non-first selects of a union to be compatible
by names with the columns of the first select. It will allow to use copies
of the same expression pushed into having clauses of different selects.
*/
if (sl != first_sl)
{
DBUG_ASSERT(sl->item_list.elements == first_sl->item_list.elements);
List_iterator_fast<Item> it(sl->item_list);
List_iterator_fast<Item> nm_it(unit->types);
Item * item;
while((item= it++))
{
item->share_name_with(nm_it++);
}
}
/*
Transform the references to the 'derived' columns from the condition
pushed into the having clause of sl to make them usable in the new context