在 DB2 查询中使用局部变量？

Question

我正在尝试编写一个使用局部变量的 DB2 查询。我真的只是想让查询更容易维护运行.

这是基本查询：

WITH MYTAB (CustomerId, VisitID, Sale, DateTime) 
AS ( VALUES   (1, 1, 'Y', '2021-04-23 20:16:00'::TIMESTAMP) , 
(1, 3, 'N', '2021-04-23 21:16:00'::TIMESTAMP) , 
(2, 2, 'N', '2021-04-24 20:16:00'::TIMESTAMP) , 
(2, 4, 'Y', '2021-04-25 20:16:00'::TIMESTAMP) , 
(2, 6, 'N', '2021-04-25 23:16:00'::TIMESTAMP) , 
(3, 5, 'Y', '2021-04-23 20:16:00'::TIMESTAMP) , (
3, 7, 'N', '2021-05-23 20:16:00'::TIMESTAMP) )  

SELECT * 
FROM MYTAB A  
WHERE DateTime > '2021-04-24'

如何使用变量来编写同样的语句？以下不会运行但给出思路：

WITH MYTAB (CustomerId, VisitID, Sale, DateTime) 
AS ( VALUES   (1, 1, 'Y', '2021-04-23 20:16:00'::TIMESTAMP) , 
(1, 3, 'N', '2021-04-23 21:16:00'::TIMESTAMP) , 
(2, 2, 'N', '2021-04-24 20:16:00'::TIMESTAMP) , 
(2, 4, 'Y', '2021-04-25 20:16:00'::TIMESTAMP) , 
(2, 6, 'N', '2021-04-25 23:16:00'::TIMESTAMP) , 
(3, 5, 'Y', '2021-04-23 20:16:00'::TIMESTAMP) ,
(3, 7, 'N', '2021-05-23 20:16:00'::TIMESTAMP) )  

WITH VAR_START(STARTDTTM) AS (VALUES(DATE('2021-01-01')))  

SELECT * 
FROM MYTAB A,VAR_START 
WHERE DateTime > STARTDTTM

Answer 1

不确定这是否是您要问的，但您可以在一个查询中包含多个 CTE：

WITH MYTAB (CustomerId, VisitID, Sale, DateTime) AS  ( 
     VALUES  (1, 1, 'Y', '2021-04-23 20:16:00'::TIMESTAMP)     
         ,  (1, 3, 'N', '2021-04-23 21:16:00'::TIMESTAMP) 
         ,  (2, 2, 'N', '2021-04-24 20:16:00'::TIMESTAMP)
) ,  VAR_START(STARTDTTM) AS ( 
     VALUES (DATE('2021-01-01') )
)          
SELECT *  
FROM MYTAB A, VAR_START     
WHERE DateTime > STARTDTTM

如果要使用变量，可以使用匿名块或存储过程。另一种选择是使用 returns 和 table 并将参数作为参数的函数。

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