Commit 5b09d7a5 authored by unknown's avatar unknown
Browse files

BUG#16798: Merge into 5.0: s/used_tables()/!const_item()/, added comment about its effects.

parent c2377412

sql/sql_select.cc

+14 −2
Original line number Diff line number Diff line
@@ -2377,7 +2377,19 @@ merge_key_fields(KEY_FIELD *start,KEY_FIELD *new_fields,KEY_FIELD *end, 
    {

      if (old->field == new_fields->field)

      {

	if (new_fields->val->used_tables())

        /*

          NOTE: below const_item() call really works as "!used_tables()", i.e.

          it can return FALSE where it is feasible to make it return TRUE.

          

          The cause is as follows: Some of the tables are already known to be

          const tables (the detection code is in make_join_statistics(),

          above the update_ref_and_keys() call), but we didn't propagate 

          information about this: TABLE::const_table is not set to TRUE, and

          Item::update_used_tables() hasn't been called for each item.

          The result of this is that we're missing some 'ref' accesses.

          TODO: OptimizerTeam: Fix this

        */

	if (!new_fields->val->const_item())

	{

	  /*

	    If the value matches, we can use the key reference.
@@ -2407,7 +2419,7 @@ merge_key_fields(KEY_FIELD *start,KEY_FIELD *new_fields,KEY_FIELD *end, 
                                new_fields->null_rejecting);

	}

	else if (old->eq_func && new_fields->eq_func &&

		 ((!old->val->used_tables() && old->val->is_null()) || 

		 ((old->val->const_item() && old->val->is_null()) || 

                  new_fields->val->is_null()))

	{

	  /* field = expression OR field IS NULL */