SQL Server：对Oracle（11g）而不是12c的前1个查询

Question

这是SQL Server中的一条SQL语句

SELECT 
    a.EMPNUM,
    (SELECT TOP 1 NAMEKO 
     FROM PA0001 
     WHERE COMPCD = a.COMPCD 
       AND EMPNUM = a.LASTUP 
     ORDER BY EDDATE DESC) AS LASTNM,
    (SELECT TOP 1 NAMEKO 
     FROM PA0001 
     WHERE COMPCD = a.COMPCD 
       AND EMPNUM = a.FRSTUP 
     ORDER BY EDDATE DESC) AS FIRSNM
FROM PA0000 a 

然后，我尝试将其应用于Oracle 11g（而不是支持top n查询的Oracle 12c）

SELECT 
    empnum,  
    (SELECT NAMEKO 
     FROM 
          (SELECT NAMEKO 
           FROM PA0001 
           WHERE COMPCD = a.COMPCD 
             AND EMPNUM = a.FRSTUP 
           ORDER BY EDDATE DESC) 
     WHERE ROWNUM = 1) AS FRSTNM,  
    (SELECT NAMEKO 
     FROM 
          (SELECT NAMEKO 
           FROM PA0001 
           WHERE COMPCD = a.COMPCD 
             AND EMPNUM = a.LASTUP 
           ORDER BY EDDATE DESC) 
     WHERE ROWNUM = 1) AS LASTNM
FROM PA0000 a

然后我得到一个错误

ORA-00904：“ A”。“ FRSTUP”：无效的标识符。

如何重写针对Oracle的查询？

Answer 1

首先，您需要向表PA0000添加别名“ a”以避免错误ORA-00904: "A"."FRSTUP": invalid identifier.

Answer 2

使用rownum = 1将选择一个不依赖于order by子句的随机值（而不是如何在磁盘上对齐块）

12c具有此功能（ FETCH FIRST {n} ROWS ONLY子句）

在11.2及更低版本中，使用row_number（）是最方便的方法

选择在架构中创建的最新对象（单个）的示例：

select *
  from (select user_objects.object_name,
               user_objects.object_id,
               user_objects.created,
               row_number () over (order by user_objects.created desc) as rn
          from user_objects) view_uo
 where view_uo.rn = 1

查看最新的10个对象将是rn <= 10

然后只需修改它以包括您的选择。

Answer 3

根据我对您问题的理解，您可以通过使用level, connect by prior来实现结果，按以下方式进行level, connect by prior ：

SELECT EMPNO FROM EMP WHERE HIREDATE IN
(SELECT MAX(HIREDATE) FROM EMP WHERE LEVEL<=1 CONNECT BY PRIOR HIREDATE>HIREDATE GROUP BY LEVEL) ORDER BY HIREDATE DESC; 

希望这能解决您的要求...