Question

我有3张桌子

GstElement *pipeline_2= gst_parse_launch("udpsrc port=20000 ! application/x-rtp,encoding-name=JPEG,payload=26 ! rtpjpegdepay ! jpegparse ! jpegdec ! videoconvert ! videoscale ! ximagesink  name=mySink", NULL);

GstElement *sink = gst_bin_get_by_name((GstBin*)pipeline_2,"mySink");

QWidget *window = new QWidget();
window->setWindowTitle("udpsrc video stream");
window->resize(700, 700);

WId xwinid = window->winId();
gst_video_overlay_set_window_handle (GST_VIDEO_OVERLAY (sink), (guintptr)xwinid);

window->show();
GstStateChangeReturn sret = gst_element_set_state (pipeline_2, GST_STATE_PLAYING);

现在我需要使用适当的数据来获得最高薪水行。

像Emp id 1一样，最高工资= 30,0000，因此从a / c表中获取整行id = 2 Emp id 2最高工资= 20,000，因此从空调表中获取整行id = 3

我尝试

Employee
---------------
ID Name
1  John 
2  Kelly
3  Leo

Dept
-------
ID  Name
1   Finance
2   A/c
3   Marketing


Accout
--------------------
Id EmpId Dept Sal
1   1     1    25,000
2   1     2    30,000
3   2     2    20,000
4   2     1    15,000
5   3     3    20,000

所以我得到的结果是

SELECT E.id,E.name AS emp_name,D.name AS dept_name,
        A.Dept as dept_id,max(A.sal) AS max_sal 
FROM Accout A 
    JOIN Employee E ON A.EmpId = E.ID 
    JOIN Dept D ON A.Dept = D.Id 
Group by EmpId

但是我需要这样的结果

Id  emp_name dept_name dept_id max_sal
1     John     Finance   1      30,000
2     Kelly     A/c      2      20,000
3     Leo    Marketing   3      20,000

请让我知道怎么可能，这样我才能获得正确的输出。

谢谢。

Answer 1

我使用GROUP BY而不是使用ORDER BY，因为您说过您只想从最高到最低薪水，另外我还删除了max()：

SELECT E.id
        E.name AS emp_name,
        D.name AS dept_name,
        A.DeptId as dept_id,
        A.sal AS max_sal
FROM Account A
JOIN Employee E ON A.EmpId = E.ID
JOIN Dept D ON A.DeptId = D.Id
ORDER BY max_sal DESC
LIMIT 3

如果要限制返回的行，可以使用LIMIT

Answer 2

您需要先找到最高薪水行，然后再与其他表连接。该查询将为您工作。

SELECT 
    E.id, E.name AS emp_name, D.name AS dept_name, A.Dept AS dept_id, max_sal
FROM
    Accout A
    JOIN
    (SELECT 
        EmpId, MAX(sal) AS max_sal FROM
        Accout GROUP BY EmpId
    ) B ON A.EmpId = B.EmpId AND A.sal = B.max_sal
    JOIN Employee E ON A.EmpId = E.ID
    JOIN Dept D ON A.Dept = D.Id;

根据MySQL中的明智方法获取最高的Sal行

2 个答案: