Method prepare

sql/sql_update.cc:1912–2061

*/

int multi_update::prepare(List<Item> &not_used_values,
			  SELECT_LEX_UNIT *lex_unit)

{
  TABLE_LIST *table_ref;
  SQL_I_List<TABLE_LIST> update_list;
  Item *item;
  List_iterator_fast<Item> field_it(*fields);
  List_iterator_fast<Item> value_it(*values);
  uint i, max_fields;
  uint leaf_table_count= 0;
  List_iterator<TABLE_LIST> update_targets_iter(update_targets);
  DBUG_ENTER("multi_update::prepare");

  if (prepared)
    DBUG_RETURN(0);
  prepared= true;

  thd->count_cuted_fields= CHECK_FIELD_WARN;
  thd->cuted_fields=0L;
  THD_STAGE_INFO(thd, stage_updating_main_table);

#ifdef WITH_WSREP
  if (WSREP(thd) &&
      (wsrep_max_ws_rows || wsrep_max_ws_size != WSREP_MAX_WS_SIZE))
  {
    int trans{0};
    while (TABLE_LIST *tablel= update_targets_iter++)
      trans|= 1 << tablel->table->file->has_transactions_and_rollback();
    update_targets_iter.rewind();
    /* In multi-table update Galera does not support update to both
       transactional and non-transactional engines if write-set
       size is limited. */
    if (trans == 3)
    {
      my_error(ER_GALERA_REPLICATION_NOT_SUPPORTED, MYF(0));
      push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
                          ER_GALERA_REPLICATION_NOT_SUPPORTED,
                          "Galera does not support multi-table update"
                          " to both transactional and non-transactional engines"
                          " if write-set size is limited.");
      DBUG_RETURN(1);
    }
  }
#endif /* WITH_WSREP */

  /*
    We gather the set of columns read during evaluation of SET expression in
    TABLE::tmp_set by pointing TABLE::read_set to it and then restore it after
    setup_fields().
  */
  while ((table_ref= update_targets_iter++))
  {
    TABLE *table= table_ref->table;
    DBUG_ASSERT(table->read_set == &table->def_read_set);
    table->read_set= &table->tmp_set;
    bitmap_clear_all(table->read_set);
  }