最近有学生在问删除表中重复记录问题，本人对此问题曾做过一些研究，现在做一个总结，算是抛砖引玉吧。
另外本文只讨论用SQL语句来解决问题，至于用VFP代码来做，以前已有前辈做了完整的示例，就不重复了。
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本文总结了四种常用的部分删除重复记录（不全删除，有条件的保留）场景：
有一个表 [jlzz1] ，原始记录如下：


情况介绍完毕。下面开始出题：
1、      以学籍号为判断依据，相同学籍号的重复记录，删除其最后一条。

DELETE FROM jlzz1 ;
      WHERE jlzz1.id IN ( ;
    SELECT m2.mid ;
      FROM ( ;
               SELECT xjh, ;
                      xm, ;
                      max(id) AS mid ;
                 FROM jlzz1 ;
                WHERE jlzz1.xjh IN ( ;
                          SELECT cChongfu.xjh ;
                            FROM ( ;
                                     SELECT jlzz1.xjh, ;
                                            jlzz1.xm, ;
                                            count( * ) AS ts ;
                                       FROM jlzz1 ;
                                      GROUP BY xjh, ;
                                               xm ;
                                     HAVING ts > 1 ;
                                 ) AS cChongfu ;
                      )  GROUP BY xjh, ;
                         xm ;
           )  AS m2 )

运行后效果：

2、      以学籍号为判断依据，相同学籍号的重复记录，删除首条。

DELETE FROM jlzz1 ;
      WHERE jlzz1.id IN ( ;
    SELECT m2.mid ;
      FROM ( ;
               SELECT xjh, ;
                      xm, ;
                      min(id) AS mid ;
                 FROM jlzz1 ;
                WHERE jlzz1.xjh IN ( ;
                          SELECT cChongfu.xjh ;
                            FROM ( ;
                                     SELECT jlzz1.xjh, ;
                                            jlzz1.xm, ;
                                            count( * ) AS ts ;
                                       FROM jlzz1 ;
                                      GROUP BY xjh, ;
                                               xm ;
                                     HAVING ts > 1 ;
                                 ) AS cChongfu ;
                      )  GROUP BY xjh, ;
                         xm ;
           )  AS m2 )

运行后效果：

3、      以学籍号为判断依据，相同学籍号的重复记录，只保留最后一条。

DELETE FROM jlzz1 ;
      WHERE jlzz1.id NOT IN ( ;
    SELECT m2.mid   FROM ( ;
               SELECT xjh,xm,max(id) AS mid ;
                 FROM jlzz1 ;
                GROUP BY xjh, xm ) AS m2)

运行后效果：

4、      以学籍号为判断依据，相同学籍号的重复记录，只保留首条。

DELETE FROM jlzz1 ;
      WHERE jlzz1.id NOT IN ( ;
    SELECT m2.mid   FROM ( ;
               SELECT xjh,xm,min(id) AS mid ;
                 FROM jlzz1 ;
                GROUP BY xjh, xm ) AS m2)

运行后效果：

附：凡有重复记录的，一律删除（不保留）：

DELETE FROM jlzz1 ;
      WHERE jlzz1.xjh  IN ( ;
    SELECT m2.xjh   FROM ( ;
               SELECT xjh,xm,count(*) AS ts ;
                 FROM jlzz1 ;
                GROUP BY xjh, xm having ts>1 ) AS m2)

运行后效果：

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欢迎提出批评和建议。
为了　练习方便，干脆把　表也传一个上来：

[此贴子已经被作者于2017-12-28 11:49编辑过]