mysql实现查重只留一个的方法：首先通过“select * from”查找表中多余的重复记录；然后通过“delete from”删除重复数据，并只保留一个数据即可。
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mysql 删除重复数据只保留一条记录
删除重复数据保留name中id最小的记录
delete from order_info where id not in (select id from (select min(id) as id from order_info group by order_number) as b);
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delete from table where id not in (select min(id) from table group by name having count(name)>1) and id in (select id group by name having count(name)>1)
(注意：HAVING 子句对 GROUP BY 子句设置条件的方式与 WHERE 和 SELECT 的交互方式类似。WHERE 搜索条件在进行分组操作之前应用；而 HAVING 搜索条件在进行分组操作之后应用。HAVING 语法与 WHERE 语法类似，但 HAVING 可以包含聚合函数。HAVING 子句可以引用选择列表中显示的任意项。)
扩展：
SQL：删除重复数据，只保留一条用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（peopleId）来判断
select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
2、删除表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断，只留有rowid最小的记录
delete from people where peopleName in (select peopleName from people group by peopleName having count(peopleName) > 1) and peopleId not in (select min(peopleId) from people group by peopleName having count(peopleName)>1)
3、查找表中多余的重复记录（多个字段）
select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 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
delete from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>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
select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
6.消除一个字段的左边的第一位：
update tableName set [Title]=Right([Title],(len([Title])-1)) where Title like '村%'
7.消除一个字段的右边的第一位：
update tableName set [Title]=left([Title],(len([Title])-1)) where Title like '%村'
8.假删除表中多余的重复记录（多个字段），不包含rowid最小的记录
update vitae set ispass=-1 where peopleId in (select peopleId from vitae group by peopleId,seq having count(*) > 1) and seq in （select seq from vitae group by peopleId,seq having count(*) > 1） and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
