mysql 用行号rownum更新顺序号字段

UPDATE customer 
INNER JOIN (SELECT
    @row_number:=CASE
        WHEN @customer_no = s.DepartmentId THEN @row_number + 1 
        ELSE 1
    END AS rowNum,
    s.id
FROM
    customer s, (SELECT @row_number:=0, @customer_no:=0) AS t
ORDER BY
    s.DepartmentId,s.CreatedTime)  afterOrder
on customer.id=afterOrder.id

set customer.OrderNo=afterOrder.rowNum