SQL 复习 01

简单复习了一下 SQL，记录一下

速查表

例子

示例表：

/* Employee */
+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Henry | 80000  | 2            |
| 3  | Sam   | 60000  | 2            |
| 4  | Max   | 90000  | 1            |
+----+-------+--------+--------------+

/* Department */
+----+----------+
| Id | Name     |
+----+----------+
| 1  | IT       |
| 2  | Sales    |
+----+----------+

/* 最直接的思路就是一层一层的嵌套子查询了，但是可读性一般，待更新... */
SELECT 
    DName AS Department,
    Name AS Employee,
    Salary
FROM (
    SELECT 
        Name, DName, Salary,
        RANK() OVER (PARTITION BY DName ORDER BY Salary DESC) as Ranking
    FROM (
        SELECT * FROM Employee 
        INNER JOIN 
        (SELECT Name AS Dname, Id AS DId FROM Department)
        AS d 
        ON d.DId = Employee.departmentId
    ) as joined
)
AS ranked
WHERE ranked.Ranking = 1;

/* result */
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| Sales      | Henry    | 80000  |
+------------+----------+--------+

参考

https://github.com/datawhalechina/team-learning-sql