SQL 从同一个 table 中获取不同值的查询

Question

假设我有这个 table: employeetable:

empid	joindate	location	HRupdatedate	Changes
1	2002-01-05	Delhi	2021-03-01	New
2	2009-09-09	Mumbai	2021-03-05	New
1	2010-06-27	Hyderabad	2021-03-03	Transfer
2	2015-11-02	Delhi	2021-03-06	Transfer
3	2020-01-01	Mumbai	2021-03-06	New
4	2007-07-30	Delhi	2021-03-04	New

我想从这个 table 中获取数据，其中 (1,2,4) 是空的。那将 return:

empid	joindate	location	HRupdatedate	Changes
1	2002-01-05	Delhi	2021-03-01	New
2	2009-09-09	Mumbai	2021-03-05	New
1	2010-06-27	Hyderabad	2021-03-03	Transfer
2	2015-11-02	Delhi	2021-03-06	Transfer
4	2007-07-30	Delhi	2021-03-04	New

但我只需要没有重复条目的最新记录：

empid	joindate	location	HRupdatedate	Changes
1	2010-06-27	Hyderabad	2021-03-03	Transfer
2	2015-11-02	Delhi	2021-03-06	Transfer
4	2007-07-30	Delhi	2021-03-04	New

如何实现？

Answer 1

您可以使用top with ties

select top(1) with ties *
from employeetable
where empid in (1,2,4)
order by row_number() over(partition by empid order by joindate desc)

Answer 2

您可以使用 WHERE 子句轻松实现此目的。

select * from  
employeetable et1
where 
    joindate = (
        select max(joindate)
            from employeetable et2 
            where et1.empid = et2.empid
    ) 
    and 
    empid in (1,2, 4);

或获得更精确的结果

select * from  
employeetable et1
where 
    joindate = (
        select max(joindate)
            from employeetable et2 
            where et1.empid = et2.empid
    ) 
    and 
    HRupdatedate = (
        select max(HRupdatedate)
            from employeetable et2 where et1.empid = et2.empid
    )
    and 
    empid in (1,2, 4);

SQL 从同一个 table 中获取不同值的查询

SQL query to fetch distinct values from same table

sql

sql-server

distinct

duplicates