Method initialize_tables

sql/sql_update.cc:2171–2318

*/

bool
multi_update::initialize_tables(JOIN *join)
{
  TABLE_LIST *table_ref;
  DBUG_ENTER("initialize_tables");

  if (unlikely((thd->variables.option_bits & OPTION_SAFE_UPDATES) &&
               error_if_full_join(join)))
    DBUG_RETURN(1);
  if (join->implicit_grouping ||
      join->select_lex->have_window_funcs())
  {
    my_error(ER_INVALID_GROUP_FUNC_USE, MYF(0));
    DBUG_RETURN(1);
  }
  main_table=join->join_tab->table;
  table_to_update= 0;

  /* Any update has at least one pair (field, value) */
  DBUG_ASSERT(fields->elements);
  /*
   Only one table may be modified by UPDATE of an updatable view.
   For an updatable view first_table_for_update indicates this
   table.
   For a regular multi-update it refers to some updated table.
  */ 
  TABLE *first_table_for_update= ((Item_field *) fields->head())->field->table;

  /* Create a temporary table for keys to all tables, except main table */
  for (table_ref= update_tables; table_ref; table_ref= table_ref->next_local)
  {
    TABLE *table=table_ref->table;
    uint index= table_ref->shared;
    List<Item> temp_fields;
    ORDER     group;
    TMP_TABLE_PARAM *tmp_param;

    table->file->prepare_for_modify(true, true);

    if (ignore)
      table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);
    if (table == main_table)			// First table in join
    {
      if (safe_update_on_fly(thd, join->join_tab, table_ref, all_tables))
      {
	table_to_update= table;			// Update table on the fly
        has_vers_fields= table->vers_check_update(*fields);
	continue;
      }
    }
    table->prepare_for_position();
    join->map2table[table->tablenr]->keep_current_rowid= true;

    /*
      enable uncacheable flag if we update a view with check option
      and check option has a subselect, otherwise, the check option
      can be evaluated after the subselect was freed as independent
      (See full_local in JOIN::join_free()).