mysql函数if语句

BEGIN
    declare result tinyint;
    set result=0;
    if period=0 then
        if date=periodData then
            set result=1;
        end if;
    elseif period=1 then
        set result=1;
    elseif period=2 then
        if WEEKDAY(date)+1=periodData then
            set result=1;
        end if;
    elseif period=3 then
        if DAYOFMONTH(date)=periodData then
            set result=1;
        end if;
　　else
　　　　if DAYOFMONTH(date)=periodData then
            set result=1;
        end if;
    end if;
    RETURN result;
END