我得到以下错误：
1064-sql语法；mysql server返回timestamp deterministic begin declare dt\u act timestamp；选择1号线
这是我的密码：

DROP FUNCTION IF EXISTS NewProc;
DELIMITER //
CREATE  FUNCTION NewProc(f_test varchar)
 RETURNS timestamp deterministic
BEGIN

DECLARE dt_act timestamp;
    select cast((case
when str_to_date(activation_date,'%d-%M-%Y') is not null then date_format(str_to_date(activation_date,'%d-%M-%Y'),'%Y-%m-%d') 
when str_to_date(activation_date,'%d-%m-%Y') is not null then date_format(str_to_date(activation_date,'%d-%m-%Y'),'%Y-%m-%d')
ELSE
date_format(str_to_date(activation_date,'%Y-%M-%d'),'%Y-%m-%d')
end) as timestamp ) into dt_act from abc where phone_no =f_test;

    RETURN dt_act;
END //

DELIMITER ;

错误：
1064-您的sql语法有错误；检查与您的mysql服务器版本相对应的手册，以获得使用near'）returns timestamp deterministic begin declare dt\u act timestamp的正确语法；选择1号线