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一. 查找重复记录
1. 查找全部重复记录
Select * From 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)
2. 过滤重复记录(只显示一条)
Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)
注：此处显示ID最大一条记录
二. 删除重复记录
1. 删除全部重复记录（慎用）
Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)
2. 保留一条（这个应该是大多数人所需要的）
Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)
注：此处保留ID最大一条记录
delete from 表名 where rowid in (select rowid from 表名 order by 字断 desc limit 条数 offset 从第几行)
"TRUNCATE table ‘表名‘"; "drop table ‘表名‘";
查找的字断是字串时用法如下
sprintf(sql, "SELECT * FROM GroupTable where gid==‘%s‘ ORDER BY gid asc", [gid UTF8String]);
并列条件如下：
sprintf(sql, "SELECT * FROM FriendTable where type==%d AND uid==%s ORDER BY name asc",type, [uidUTF8String]);
获取所有字断中如果重复就可获取一条最小的ID
sprintf(sql, "SELECT * FROM CarTable where Id In (SELECT Min(Id) form CarTable Group By 字断) ORDER BY carId asc");
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原文地址：http://www.cnblogs.com/mumoozhu/p/4582833.html
