现有一个存储过程：

BEGIN

DECLARE s int DEFAULT 0;
DECLARE mid VARCHAR(10);
DECLARE realname VARCHAR(20);
DECLARE mobile VARCHAR(20);
DECLARE email VARCHAR(50);

DECLARE user CURSOR FOR select id, realname, mobile, email from tb_user where status = 1;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET s=1;

open user;
fetch user into mid, realname, mobile, email;
WHILE s<>1 DO

UPDATE tb_b set title = REPLACE(title,mobile,'*') where uid = mid;

fetch user into mid, realname, mobile, email;
END WHILE;

close user;
END
循环中的update语句中，replace替换，会把整个标题替换成空值，我是想只把title字段中的mobile替换成*。这里的mobile是结果集的值，该怎么写呢（tb_user表中的id也是VARCHAR类型）？