区别在SQL查询中产生重复值

Question

在我的数据库中，有来自同一员工的多个条目，因此我希望通过识别自动编号字段来获取最新条目。但是在eno中使用下面带有distinct的sql代码会导致重复的条目。

SELECT distinct(eNo), auto_num from mc_employee 
order by auto_num

关于我做错了什么的线索？

Answer 1

DISTINCT未应用于SELECT子句的特定字段。它更适用于所有 SELECT子句中的字段。

如果您想获得最新记录，可以使用ROW_NUMBER：

SELECT eNo, auto_num
FROM (
   SELECT eNo, auto_num,
          ROW_NUMBER() OVER (PARTITION BY eNo ORDER BY auto_num DESC) AS rn 
   from mc_employee ) AS t
WHERE t.rn = 1
ORDER BY auto_num

Answer 2

尝试以下查询：

SELECT eNo,auto_num 
FROM
( SELECT eNo, auto_num, ROW_NUMBER() OVER(PARTITION BY eNo ORDER BY auto_num DESC) as RN
  FROM mc_employee
)T
WHERE RN=1

Answer 3

最简单的方法是TOP(1) WITH TIES ... ORDER BY ROW_NUMBER() OVER ()

SELECT TOP(1) WITH TIES eNo, auto_num
FROM mc_employee
ORDER BY ROW_NUMBER() OVER (PARTITION BY eNo ORDER BY auto_num DESC)

Answer 4

这也是一个子选择解决方案：

SELECT distinct(dist.eNo), (select max(auto_num) from mc_employee i where i.eNo=dist.eNo) auto_num
from mc_employee dist
order by auto_num