帮助与SQL连接

Question

我有两个表：

表1： ID，PersonCode，名称，

表2： ID，Table1ID，地点，ServiceDate

我有一个查询将表1添加到table1.ID = table2.Table1ID其中PersonCode ='XYZ'

我想要做的是返回Table1.PersonCode，Table1.Name，Table2.Location，Table2.ServiceDate，我不想要所有的行，在表2中，我只对t感兴趣他为每个位置排列最近的ServiceDate。我会如何去做这件事？

Answer 1

事情是这样的：

SELECT 
    Table1.PersonCode, Table1.Name, Table2.Location, MAX(Table2.ServiceDate) 
FROM 
    Table1 
    INNER JOIN Table2 on Table1.ID = Table2.Table1ID 
WHERE 
    TABLE1.PersonCode = 'XYZ' 
GROUP BY 
    Table1.PersonCode,Table1.Name, Table2.Location 

Answer 2

使用MAX（ServiceDate）

Answer 3

尝试：

select Table1.PersonCode,Table1.Name, Table2.Location, Table2.ServiceDate 
from Table1 
join Table2 on table1.ID = table2.Table1ID 
where table1.PersonCode = 'XYZ' 
and table2.ServiceDate = (select max(t2.ServiceDate) 
          from table2 t2 
          where t2.table1ID = table2.table1ID 
          and t2.location = table2.location 
         ); 

Answer 4

我会用一个INNER JOIN并选择第一个记录，在下令在反向记录基于Table2.ServiceDate的时间顺序。

SELECT TOP 1 
    Table1.PersonCode, Table1.Name, Table2.Location, Table2.ServiceDate 
FROM 
    Table1 
    INNER JOIN Table2 on Table1.ID = Table2.Table1ID 
WHERE 
    TABLE1.PersonCode = 'XYZ' 
ORDER BY Table2.ServiceDate DESC 
GROUP BY 
    Table1.PersonCode,Table1.Name, Table2.Location