在WHERE子句中使用别名

Question

我正在执行以下查询，并为所有列使用别名。我用命名了别名。因为这是必需的。现在，我想直接在where子句中引用别名，我的操作如下所示：

SELECT pt.prod_desc AS"PROD_DESC",
 (
CASE
WHEN pt.prod_level='2'
THEN 'Product'
WHEN pt.prod_level='4'
THEN 'Sub-Product'
WHEN pt.prod_level='5'
THEN 'Service'
ELSE 'N/A'
 END)         AS"PROD_LEVEL",
prod_id      AS "PROD_ID",
isactive     AS "IsActive",
updt_usr_sid AS "UPDT_USR_SID",
updt_ts      AS "UPDT_TS",
(
CASE
WHEN pt.prod_level='5'
THEN parent_prod_id
ELSE NULL
  END) AS ".SUB_PROD_ID",
(
 CASE
  WHEN pt.prod_level='5'
  THEN
  (SELECT prod_desc FROM dims_prod_type A WHERE A.prod_id= pt.parent_prod_id
  )
  ELSE 'N/A'
 END ) AS ".SUB_PROD_DESC",
 (
CASE
WHEN pt.prod_level='4'
THEN parent_prod_id
WHEN pt.prod_level='5'
THEN
  (SELECT parent_prod_id
  FROM dims_prod_type A
  WHERE A.prod_id= pt.parent_prod_id
   )
 ELSE NULL
   END) AS ".PRNT_PROD_ID",
(
 CASE
 WHEN pt.prod_level='4'
THEN
   (SELECT prod_desc FROM dims_prod_type A WHERE A.prod_id=pt.parent_prod_id
   )
  WHEN pt.prod_level='5'
THEN
   (SELECT prod_desc
   FROM dims_prod_type A
  WHERE A.prod_id IN
    (SELECT B.parent_prod_id
    FROM dims_prod_type B
    WHERE b.prod_id=pt.parent_prod_id
    )
  )
 ELSE 'N/A'
 END)AS ".PRNT_PROD_DESC"
FROM dims_prod_type pt
WHERE pt.".PRNT_PROD_ID" like 'A%';

但是，当我执行此操作时，出现以下错误：

    SQL Error: ORA-00904: "PT".".PRNT_PROD_ID": invalid identifier
     00904. 00000 -  "%s: invalid identifier"

我知道SQL首先执行where子句，因此这就是错误的原因。但是我该如何解决呢？有什么建议吗？

Answer 1

您已经知道不能在where子句中使用别名，但这仅适用于相同级别的SQL。您可以将查询包装在外部查询中：

SELECT *
FROM (
  SELECT pt.prod_desc AS"PROD_DESC",
  ...
   END)AS ".PRNT_PROD_DESC"
  FROM dims_prod_type pt
)
WHERE ".PRNT_PROD_ID" like 'A%';

唯一的选择是重复case在where子句中生成该列的整个过程，这对于如此复杂的事情将是不愉快的。