sql删除重复记录

Posted 2020-10-07 懵懂的菜鸟

用SQL语句,删除掉重复项只保留一条

在 SQL 中增加 HAVING 子句原因是，WHERE 关键字无法与合计函数一起使用。

 所有的合计函数如下表所示：

MIN
返回一个给定列中最小的数值
MAX
返回一个给定列中最大的数值
SUM
返回一个给定列中所有数值的总和
AVG
返回一个给定列中所有数值的平均值
COUNT
返回一个给定列中所有数值的个数
COUNT(*)
返回一个表中的行数假设我们将从employee表中搜索工资最高的列，可以使用以下的SQL语句：

SELECT max(salary), dept

FROM employee

GROUP BY dept;

这条语句将在每一个单独的部门中选择工资最高的工资。结果他们的salary和dept将被返回。SELECT dept, avg(salary) 每个部门，的平均工资

FROM employee 来自此表

GROUP BY dept 每部门只显示一个，相同部门不显示。

HAVING avg(salary) > 20000; 指定平均值大于多少的显示

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（地址）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