【⼩5聊】SqlServer基础之分组查询重复出现多条记录的SQL
语句，以及groupby。。。
【开发环境】
开发系统：Windows 10
开发语⾔：SQL Server
开发⼯具：SQL Server 2008 R2
⽂章作⽤：记录、备忘、总结、分享、理解
相互学习：号-xgwkf566
⼈⽣格⾔：勤能补拙
【主要知识点】
group by 分组
having 筛选条件
count()函数，总记录数
min()函数，最⼩值
max()函数，最⼤值
union all，记录叠加，重复不合并，但是字段必须⼀致
union和union all的区别
【知识点应⽤】
1、假如查询记录如下
select * from(
select 1 id,'语⽂' as kecheng union all
select 2 id,'数学' as kecheng union all
select 3 id,'语⽂' as kecheng union all
select 4 id,'英语' as kecheng union all
select 5 id,'语⽂' as kecheng union all
select 6 id,'数学' as kecheng
) as table_
select min(id) as minid,max(id) as maxid,count(1) as shuliang,kecheng from (
groupby分组select 1 id,'语⽂' as kecheng union all
select 2 id,'数学' as kecheng union all
select 3 id,'语⽂' as kecheng union all
select 4 id,'英语' as kecheng union all
select 5 id,'语⽂' as kecheng union all
select 6 id,'数学' as kecheng
) as table_ group by kecheng
3、结合having筛选的使⽤
select min(id) as minid,max(id) as maxid,count(1) as shuliang,kecheng from (
select 1 id,'语⽂' as kecheng union all
select 2 id,'数学' as kecheng union all
select 3 id,'语⽂' as kecheng union all
select 4 id,'英语' as kecheng union all
select 5 id,'语⽂' as kecheng union all
select 6 id,'数学' as kecheng
) as table_ group by kecheng
having count(kecheng)>2
因此，从上⾯步骤即可排查出现重复的记录
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