BUG#8804: Incorrect results for NULL IN (SELECT ...): review fixes:

  SYNOPSIS

    Item_in_subselect::single_value_transformer()

      join

      func

      join  Join object of the subquery (i.e. 'child' join).

      func  Subquery comparison creator

  DESCRIPTION

    Rewrite a single-column subquery using rule-based approach. The subquery

       oe $cmp$ (SELECT sel FROM ... WHERE subq_where HAVING subq_having)

       oe $cmp$ (SELECT ie FROM ... WHERE subq_where ... HAVING subq_having)

    First, try to convert the subquery to scalar-result subquery in one of

    the forms:

       - oe $cmp$ (SELECT MAX(...) )  // handled by Item_singlerow_subselect

       - oe $cmp$ <max>(SELECT ...)   // handled by Item_maxminsubselect

       - oe $cmp$ <max>(SELECT ...)   // handled by Item_maxmin_subselect

    If that fails, the subquery will be handled with class Item_in_optimizer, 

    Inject the predicates into subquery, i.e. convert it to:

    - If the subquery has aggregates, GROUP BY, or HAVING, convert to

       SELECT sel FROM ...  HAVING subq_having AND 

       SELECT ie FROM ...  HAVING subq_having AND 

                                   trigcond(oe $cmp$ ref_or_null_helper<ie>)

      the addition is wrapped into trigger only when we want to distinguish

      between NULL and FALSE results.

    - Else, if we don't care if subquery result is NULL or FALSE, convert to

    - Otherwise (no aggregates/GROUP BY/HAVING) convert it to one of the

      following:

       SELECT 1 ... WHERE (oe $CMP$ ie) AND subq_where

      = If we don't need to distinguish between NULL and FALSE subquery:

    - Else convert to:

        SELECT 1 FROM ... WHERE (oe $cmp$ ie) AND subq_where

       SELECT 1 WHERE ...

         WHERE  subq_where  AND trigcond((oe $CMP$ ie) OR ie IS NULL)

         HAVING subq_having AND trigcond(<is_not_null_test>(ie))

      = If we need to distinguish between those:

        SELECT 1 FROM ...

          WHERE  subq_where AND trigcond((oe $cmp$ ie) OR (ie IS NULL))

          HAVING trigcond(<is_not_null_test>(ie))

  RETURN

    RES_OK     - Transformed successfully (or done nothing?)

    RES_OK     - OK, either subquery was transformed, or appopriate

                 predicates where injected into it.

    RES_REDUCE - The subquery was reduced to non-subquery

    RES_ERROR  - Error

*/

	  we can assign select_lex->having here, and pass 0 as last

	  argument (reference) to fix_fields()

	*/

	select_lex->having=

	  join->having= (join->having ?

			 new Item_cond_and(having, join->having) :

			 having);

	select_lex->having= join->having= having;

	select_lex->having_fix_field= 1;

        /*

          we do not check join->having->fixed, because Item_and (from

bool subselect_single_select_engine::no_rows()

{ 

//  return test(!join->send_records);

  return !item->assigned();

}

  int error;

  TABLE *table= tab->table;

  DBUG_ENTER("subselect_uniquesubquery_engine::scan_table");

  empty_result_set= TRUE;

  bool is_uncorrelated= !cond || !(cond->used_tables() & OUTER_REF_TABLE_BIT);

  if (table->file->inited)

    table->file->ha_index_end();