sql - 如何重构这个 SQL 查询？

Question

我正在向 IBM DB2 服务器编写以下查询：

SELECT 
    EMPNO, 
    YEAR(CURRENT TIMESTAMP - BIRTHDATE) AS AGE,
    DENSE_RANK() OVER(ORDER BY YEAR(CURRENT TIMESTAMP - BIRTHDATE) ASC) AS RANK

FROM 
    DANDY.EMPLOYEE;

它有效，但看起来很难看，因为我正在重复表达：

YEAR(CURRENT TIMESTAMP - BIRTHDATE)

但是这样写是行不通的：

DENSE_RANK() OVER(ORDER BY AGE ASC) AS RANK

如何让它变得更好？

Answer 1

SELECT 
EMPNO, 
AGE,
DENSE_RANK() OVER(ORDER BY AGE ASC) AS RANK
FROM (SELECT EMPNO,
             YEAR(CURRENT TIMESTAMP - BIRTHDATE) AS AGE
      FROM DANDY.EMPLOYEE);

Answer 2

我知道标准ORDER BY条款通常接受列索引，但不确定它是否适用DENSE_RANK()- 也许尝试：

DENSE_RANK() OVER(ORDER BY 2 ASC) AS RANK

Answer 3

您可以使用公用表表达式 (CTE) 来获取AGE，然后AGE根据需要再次使用。

WITH
   CTEAGE AS
      (SELECT 
          YEAR(CURRENT TIMESTAMP - BIRTHDATE) AS AGE,
      FROM 
          DANDY.EMPLOYEE
      )

   SELECT 
      EMPNO, 
      CTEAGE.AGE,
      DENSE_RANK() OVER(CTEAGE.AGE ASC) AS RANK
   FROM 
      DANDY.EMPLOYEE;