mysql 自定义函数，if else

CREATE FUNCTION isRepeat1(mycode varchar(32)) RETURNS varchar(32)
    DETERMINISTIC
    COMMENT 'I_Code中index是否重复，0不重复，1 重复'
begin
	declare i varchar(32);
	set i = (select count(*) from  gqj_gqjbook where substring(I_CODE,6,18) = substring(mycode,6,18));
	if i = 1 then
		set i = 0;
	else 
		set i = 1;
	end if;
	
	return i;
end