mysql - 如何在sql中选择表的最后一行？

Question

我有来自不同表的列，这些列通过它们的公共(public)键连接起来。我想要做的是选择具有相同 ev_k 的每行的最后一个数据。请引用下表。

3489    7666    LOND                                c   i   N   10/21/2013  09:30:29
3490    7666    LOND                                c   c   N   10/21/2013  09:30:29
3491    7666    LOND                                l   i   N   10/21/2013  09:30:29
3492    7666    LOND                                l   d   N   10/21/2013  09:30:29
3493    7666    LOND                                l   c   N   10/21/2013  09:32:52
3494    7666    LOND                                i   i   N   10/21/2013
3495    7666    LOND                                i   d   N   10/21/2013  09:32:52
3496    7666    LOND                                i   p   N   10/21/2013  09:51:20
2159    6367    LOND                                c   i   N   10/21/2013  10:25:00
2160    6367    LOND                                c   c   N   10/21/2013  10:25:00
2162    6367    LOND                                l   d   N   10/21/2013  10:25:00
2161    6367    LOND                                l   i   N   10/21/2013  10:25:00
2163    6367    LOND                                l   p   N   10/21/2013  10:25:08
3371    7463    LOND                                c   i   N   10/21/2013  11:07:23
3374    7463    LOND                                l   d   N   10/21/2013  11:07:24
3373    7463    LOND                                l   i   N   10/21/2013  11:07:24
3372    7463    LOND                                c   c   N   10/21/2013  11:07:24
3377    7463    LOND                                i   d   N   10/21/2013  11:07:32
3376    7463    LOND                                i   i   N   10/21/2013  11:07:32
3375    7463    LOND                                l   c   N   10/21/2013  11:07:32
3378    7463    LOND                                i   c   N   10/21/2013  11:07:41
3380    7463    LOND                                c2  c   N   10/21/2013  11:07:42
3381    7463    LOND                                a1  i   N   10/21/2013  11:07:42
3382    7463    LOND                                a1  d   N   10/21/2013  11:07:42
3379    7463    LOND                                c2  i   N   10/21/2013  11:07:42
3383    7463    LOND                                a1  c   N   10/21/2013  11:07:51
3384    7463    LOND                                r   i   N   10/21/2013  11:07:51
3385    7463    LOND                                r   c   N   10/21/2013  11:07:52
3387    7463    LOND                                -   c   Y   10/21/2013  11:07:53
3386    7463    LOND                                -   i   N   10/21/2013  11:07:53

在提供的表中，我要检索的是以下行:

3496    7666    LOND                                i   p   N   10/21/2013  09:51:20
2163    6367    LOND                                l   p   N   10/21/2013  10:25:08
3386    7463    LOND                                -   i   N   10/21/2013  11:07:53

用于获取表上数据的脚本编写如下:

SELECT T1.KEY, T1.ev_k, T1.BRANCH, T2.THEIR_REF, T1.TYPE, T1.STATUS, T1.ISLASTSTEP, T1.FINISHDATE, T1.FINISHTIME 
FROM STEPHIST T1, BASEEVENT T2, EXEMPL30 T3
WHERE T1.EVENT_KEY = T2.KEY97
AND T2.EXEMPLAR = T3.KEY97
ORDER BY THEIR_REF, FINISHTIME;

谢谢。

Answer 1

您应该学习使用正确的 join 语法并使用表别名(它们所引用的表的缩写)。

然后，你只需要计算并加入最大时间即可:

SELECT s.KEY, s.ev_k, s.BRANCH, b.THEIR_REF, s.TYPE, s.STATUS,
       s.ISLASTSTEP, s.FINISHDATE, s.FINISHTIME 
FROM STEPHIST s JOIN
     BASEEVENT b
     ON s.EVENT_KEY = b.KEY97 JOIN
     EXEMPL30 e
     ON b.EXEMPLAR = e.KEY97 JOIN
     (SELECT s.ev_k, MAX(FINISHTIME) as maxft
      FROM STEPHIST s
      GROUP BY s.ev_k
     ) ss
     ON s.ev_k = ss.ev_k AND s.finishtime = ss.msxft
ORDER BY Tb.HEIR_REF, s.FINISHTIME;