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MDEV-6859: scalar subqueries in a comparison produced unexpected result

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When one evaluates row-based comparison like (X, Y) = (A,B), one should
first call bring_value() for the Item that returns row value. If you
don't do that and just attempt to read values of X and Y, you get stale
values.
Semi-join/Materialization can take a row-based comparison apart and
make ref access from it. In that case, we need to call bring_value()
to get the index lookup components.
This commit is contained in:
Sergei Petrunia
2016-02-09 02:31:47 +03:00
parent d443d70d06
commit b17a435069
4 changed files with 133 additions and 0 deletions
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11
sql/sql_select.cc
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@ -17580,7 +17580,18 @@ int join_read_key2(THD *thd, JOIN_TAB *tab, TABLE *table, TABLE_REF *table_ref)
}
}
/*
The following is needed when one makes ref (or eq_ref) access from row
comparisons: one must call row->bring_value() to get the new values.
*/
if (tab && tab->bush_children)
{
TABLE_LIST *emb_sj_nest= tab->bush_children->start->emb_sj_nest;
emb_sj_nest->sj_subq_pred->left_expr->bring_value();
}
/* TODO: Why don't we do "Late NULLs Filtering" here? */
if (cmp_buffer_with_ref(thd, table, table_ref) ||
(table->status & (STATUS_GARBAGE | STATUS_NO_PARENT | STATUS_NULL_ROW)))
{