Where 子句中的 if 语句

Question

我正在处理一个在“WHERE”子句中包含“IF”语句的查询。但是 PL\SQL Developer 在执行时给出了一些错误。谁能帮我正确查询？这是查询：

SELECT t.first_name,
       t.last_name,
       t.employid,
       t.status
  FROM employeetable t
 WHERE IF status_flag = STATUS_ACTIVE then t.status = 'A'
       IF status_flag = STATUS_INACTIVE then t.status = 'T'
       IF source_flag = SOURCE_FUNCTION then t.business_unit = 'production'
       IF source_flag = SOURCE_USER then t.business_unit = 'users'
   AND t.first_name LIKE firstname
   AND t.last_name LIKE lastname
   AND t.employid LIKE employeeid;

我收到错误“ORA-00920：无效的关系运算符”。

在status_flag = STATUS_ACTIVE 周围放置括号会导致错误“ORA-00907：缺少右括号”

Answer 1

你不能这样使用 IF。你可以用 AND 和 OR 做你想做的事：

SELECT t.first_name,
       t.last_name,
       t.employid,
       t.status
  FROM employeetable t
 WHERE ((status_flag = STATUS_ACTIVE   AND t.status = 'A')
     OR (status_flag = STATUS_INACTIVE AND t.status = 'T')
     OR (source_flag = SOURCE_FUNCTION AND t.business_unit = 'production')
     OR (source_flag = SOURCE_USER     AND t.business_unit = 'users'))
   AND t.first_name LIKE firstname
   AND t.last_name  LIKE lastname
   AND t.employid   LIKE employeeid;

Answer 2

CASE 可能会帮助你：

SELECT t.first_name,
       t.last_name,
       t.employid,
       t.status
  FROM employeetable t
 WHERE t.status = (CASE WHEN status_flag = STATUS_ACTIVE THEN 'A'
                        WHEN status_flag = STATUS_INACTIVE THEN 'T'
                        ELSE null END)
   AND t.business_unit = (CASE WHEN source_flag = SOURCE_FUNCTION THEN 'production'
                               WHEN source_flag = SOURCE_USER THEN 'users'
                               ELSE null END)
   AND t.first_name LIKE firstname
   AND t.last_name LIKE lastname
   AND t.employid LIKE employeeid;

CASE statement 评估多个条件以生成单个值。因此，在第一次使用中，我检查 status_flag 的值，根据它的值返回“A”、“T”或 null，并将其与 t.status 进行比较。我使用第二个 CASE 语句对 business_unit 列执行相同的操作。