oracle单引号转义

# ''yyyy-MM-dd''
declare
  num number;
begin
  select count(1) into num from user_indexes where table_name=upper('S_SALE_ORDER') and index_name=upper('S_SALE_ORDER_USER_INDEX');
  if num =0 then
    execute immediate 'CREATE INDEX S_SALE_ORDER_USER_INDEX ON S_SALE_ORDER(USERID,TO_CHAR(XSRQ,''yyyy-MM-dd''))';
  end if;
end;
/