mysql有row_number函数吗？

SET @row_number = 0;
SELECT
    (@row_number:=@row_number + 1) AS num, s.id, s.name, s.age
FROM
    student s;

SET @row_number=0, @customer_no=0;

SELECT
    @row_number:=CASE
        WHEN @customer_no = s.age THEN @row_number + 1 
        ELSE 1
    END AS num,
    @customer_no:=s.age AS stu_age,
    s.id, 
    s.name 
FROM
    student s
ORDER BY
    s.age;

SELECT
    @row_number:=CASE
        WHEN @customer_no = s.age THEN @row_number + 1 
        ELSE 1
    END AS num,
    @customer_no:=s.age AS stu_age,
    s.id, 
    s.name 
FROM
    student s, (SELECT @row_number:=0, @customer_no:=0) AS t
ORDER BY
    s.age;