如何对别名字段执行函数

Question

我在PostgreSQL中有一个视图，我正在使用COALESCE函数从表中提取第一个NOT NULL字段。即

SELECT 
SRC.SAP_SETNODE.SUBSET_CLS,
COALESCE(
    SETNODE_13.SUBSET_NAME,
    SETNODE_12.SUBSET_NAME,
    SETNODE_11.SUBSET_NAME,
    SETNODE_10.SUBSET_NAME,
    SETNODE_9.SUBSET_NAME,
    SETNODE_8.SUBSET_NAME,
    SETNODE_7.SUBSET_NAME,
    SETNODE_6.SUBSET_NAME,
    SETNODE_5.SUBSET_NAME,
    SETNODE_4.SUBSET_NAME,
    SETNODE_3.SUBSET_NAME,
    SETNODE_2.SUBSET_NAME,
    SETNODE_1.SUBSET_NAME,
    SRC.SAP_SETNODE.SUBSET_NAME,
    SRC.SAP_SETNODE.SET_NAME)
AS prctr1, 

在我有了这个字段后，我想创建一个名为prctr2的新字段，在那里我想做一个SPLIT PART&如果是LIKE"PC%"，则在prctr1字段上显示OVERLAY函数

我试图对此做一个CASE声明，大致如下：

WHEN prctr1 LIKE 'PC%' THEN split_part( overlay(prctr1 placing '00000' from 1 for 2 ),'.',1)
ELSE prctr1

但我收到一条消息，说prctr1列不存在。有办法做到这一点吗？

Answer 1

只需将主查询封装在外部查询中，然后执行CASE语句，如下所示：

   SELECT CASE WHEN prctr1 LIKE 'PC%' THEN split_part( overlay(prctr1 placing '00000' from 1 for 2 ),'.',1)
ELSE prctr1 end as pctrl1 
FROM (
SELECT 
SRC.SAP_SETNODE.SUBSET_CLS,
COALESCE(
    SETNODE_13.SUBSET_NAME,
    SETNODE_12.SUBSET_NAME,
    SETNODE_11.SUBSET_NAME,
    SETNODE_10.SUBSET_NAME,
    SETNODE_9.SUBSET_NAME,
    SETNODE_8.SUBSET_NAME,
    SETNODE_7.SUBSET_NAME,
    SETNODE_6.SUBSET_NAME,
    SETNODE_5.SUBSET_NAME,
    SETNODE_4.SUBSET_NAME,
    SETNODE_3.SUBSET_NAME,
    SETNODE_2.SUBSET_NAME,
    SETNODE_1.SUBSET_NAME,
    SRC.SAP_SETNODE.SUBSET_NAME,
    SRC.SAP_SETNODE.SET_NAME)
AS prctr1
) as foo