MDEV-24710 Uninitialized value upon CREATE .. SELECT ... VALUE...

The failure happened for group by queries when all tables where marked as
'const tables' (tables with 0-1 matching rows) and no row matched the
where clause and there was in addition a direct reference to a field.

In this case the field would not be properly reset and the query would
return 'random data' that happended to be in table->record[0].

Fixed by marking all const tables as null tables in this particular case.

Sergei also provided an extra test case for the code.

@reviewer Sergei Petrunia <psergey@askmonty.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/sql/table.h b/sql/table.h
index 3c31a6364df..6a4c6eb2a03 100644
--- a/sql/table.h
+++ b/sql/table.h
@@ -3145,6 +3145,12 @@ inline void mark_as_null_row(TABLE *table)
     bfill(table->null_flags,table->s->null_bytes,255);
 }
 
+inline void unmark_as_null_row(TABLE *table)
+{
+  table->null_row=0;
+  table->status= STATUS_NO_RECORD;
+}
+
 bool is_simple_order(ORDER *order);
 
 class Open_tables_backup;