学习笔记（MySQL巧妙的排序号）

SELECT
    e1.first_name 
FROM
    (
    SELECT
        e2.first_name,
        ( SELECT COUNT(*) FROM employees AS e3 WHERE e3.first_name <= e2.first_name ) AS rowid 
    FROM
        employees AS e2 
    ) AS e1 
WHERE
    e1.rowid % 2 = 1;

可以实现对表记录添加编号

思路： SELECT COUNT(*) FROM employees AS e3 WHERE e3.first_name <= e2.first_name