Function make_join_readinfo

sql/sql_select.cc:16352–16667

*/

static bool
make_join_readinfo(JOIN *join, ulonglong options, uint no_jbuf_after)
{
  JOIN_TAB *tab;
  uint i;
  DBUG_ENTER("make_join_readinfo");

  Json_writer_object  trace_wrapper(join->thd);
  Json_writer_array   trace_arr(join->thd, "make_join_readinfo");

  bool statistics= MY_TEST(!(join->select_options & SELECT_DESCRIBE));
  bool sorted= 1;

  join->complex_firstmatch_tables= table_map(0);

  if (!join->select_lex->sj_nests.is_empty() &&
      setup_semijoin_dups_elimination(join, options, no_jbuf_after))
    DBUG_RETURN(TRUE); /* purecov: inspected */
  
  /* For const tables, set partial_join_cardinality to 1. */
  for (tab= join->join_tab; tab != join->join_tab + join->const_tables; tab++)
    tab->partial_join_cardinality= 1; 

  JOIN_TAB *prev_tab= NULL;
  i= join->const_tables;
  for (tab= first_linear_tab(join, WITH_BUSH_ROOTS, WITHOUT_CONST_TABLES);
       tab; 
       prev_tab=tab, tab= next_linear_tab(join, tab, WITH_BUSH_ROOTS))
  {
    /*
      The approximation below for partial join cardinality is not good because
        - it does not take into account some pushdown predicates
        - it does not differentiate between inner joins, outer joins and
        semi-joins.
      Later it should be improved.
    */

    if (tab->bush_root_tab && tab->bush_root_tab->bush_children->start == tab)
      prev_tab= NULL;
    DBUG_ASSERT(tab->bush_children ||
                tab->table == join->best_positions[i].table->table);

    tab->partial_join_cardinality= join->best_positions[i].records_read *
                                   (prev_tab ?
                                    prev_tab->partial_join_cardinality : 1);
    if (!tab->bush_children)
      i++;
  }
 
  check_join_cache_usage_for_tables(join, options, no_jbuf_after);

  JOIN_TAB *first_tab;
  for (tab= first_tab= first_linear_tab(join,
                                        WITH_BUSH_ROOTS, WITHOUT_CONST_TABLES);
       tab; 
       tab= next_linear_tab(join, tab, WITH_BUSH_ROOTS))
  {
    if (tab->bush_children)