Method optimize_inner

sql/sql_select.cc:2213–2793

*/

int
JOIN::optimize_inner()
{
  DBUG_ENTER("JOIN::optimize_inner");
  subq_exit_fl= false;
  best_read= 0.0;

  DEBUG_SYNC(thd, "before_join_optimize");
  THD_STAGE_INFO(thd, stage_optimizing);
#ifndef DBUG_OFF
  dbug_join_tab_array_size= 0;
#endif

  // rownum used somewhere in query, no limits and it is derived
  if (unlikely(thd->lex->with_rownum &&
               select_lex->first_cond_optimization &&
               select_lex->master_unit()->derived))
    optimize_upper_rownum_func();

  do_send_rows = (unit->lim.get_select_limit()) ? 1 : 0;

  set_allowed_join_cache_types();
  need_distinct= TRUE;

  Json_writer_object trace_wrapper(thd);
  Json_writer_object trace_prepare(thd, "join_optimization");
  trace_prepare.add_select_number(select_lex->select_number);
  Json_writer_array trace_steps(thd, "steps");

  if (select_lex->opt_hints_qb)
    select_lex->opt_hints_qb->trace_hints(thd);

  /*
    Needed in case optimizer short-cuts,
    set properly in make_aggr_tables_info()
  */
  fields= &select_lex->item_list;

  if (select_lex->first_cond_optimization)
  {
    //Do it only for the first execution
    /* Merge all mergeable derived tables/views in this SELECT. */
    if (select_lex->handle_derived(thd->lex, DT_MERGE))
      DBUG_RETURN(TRUE);  
    table_count= select_lex->leaf_tables.elements;
  }

  if (select_lex->first_cond_optimization &&
      transform_in_predicates_into_in_subq(thd))
    DBUG_RETURN(1);

  /*
    Update used tables after all handling derived table procedures
    After this call, select_lex->select_list_tables contains the table
    bits of all items in the select list (but not bits from WHERE clause or
    other items).
  */
  select_lex->update_used_tables();