用SQL语句,删除掉重复项只保留一条
在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢
1、查找表中多余的重复记录，重复记录是根据单个字段（id）来判断
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/<em> 表中不是能过ID进行自增，id是城市的编号 </em>/ SELECT <em> FROM Community WHERE id IN ( SELECT id FROM Community GROUP BY id HAVING count(id)> 1 ) order by id ; /</em> 通过id进行排序 */ |
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/<em> 表中不是能过ID进行自增，id是城市的编号 </em>/ SELECT <em> FROM Community WHERE id IN(SELECT id FROM Community GROUP BY id HAVING count(id)> 1) order by id ; /</em> 通过id进行排序 */ |
2、删除表中多余的重复记录，重复记录是根据单个字段（Comm_Name）来判断，只留有rowid最小的记录
MYSQL中无法执行这段代码，请使用下面的代码
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1093 - You can't specify target table 'Community' for update in FROM clause |
表中字段Comm_ID 为自增ID
DELETE * FROM Community WHERE Comm_Name IN ( SELECT Comm_Name FROM Community GROUP BY Comm_Name HAVING count(Comm_Name )>1) AND Comm_ID NOT IN ( SELECT min(Comm_ID) FROM Community GROUP BY Comm_Name HAVING count ( Comm_Name )>1 );
MYSQL数据库的操作
3、查找表中多余的重复记录（多个字段）
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SELECT <em> FROM Community c WHERE (c.id, c.name) IN (SELECT id, name FROM Community GROUP BY id, name HAVING count(</em>)>1) |
4、删除表中多余的重复记录（多个字段），只留有rowid最小的记录
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DELETE FROM Community c WHERE (c.id, c.name) IN (SELECT id, name FROM Community GROUP BY id, name HAVING count(<em>)>1) AND rowid NOT IN ( SELECT min(rowid) FROM Community GROUP BY id, name HAVING count(</em>)>1 ) |
5、查找表中多余的重复记录（多个字段），不包含rowid最小的记录
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SELECT <em> FROM Community c WHERE (c.id,c.name) IN (SELECT id,name FROM Community GROUP BY id,name HAVING count(</em>)>1) AND rowid NOT IN (SELECT min(rowid) FROM Community GROUP BY id,name HAVING count(*) > 1); |
