Question

我正在使用DB2，如果数据库中没有存在IN子句中存在的ID的行，我想要返回虚拟值

SELECT A.EmpName, A.EmpId,B.Address, C.OrgCode
FROM Employee A
    join Address B on A.EmpId = B.EmpId 
    join Organization C on A.EmpId = C.EmpId
where A.SecretId in ('1', '2', '3', '4', '5');

我在数据库中使用Secret Id 1,2,3,4的员工但不是5但我需要的结果如下所示

EmpId   EmpName Address OrgCode
  1        A      XXX     23
  2        B      YYY     44
  3        C      ZZZZ    21
  4        D      KKK     23
  5       N/A     N/A     N/A

我需要用一些虚拟值填充值。我从其他系统获取秘密ID列表。

请帮助我实现这一目标。

我使用DB2作为我的数据库。

Answer 1

您需要一个left join，并从您没有的价值开始：

SELECT e.EmpName, el.EmpId, a.Address, o.OrgCode
FROM (SELECT 1 as EmpId FROM sysibm.sysdummy1 UNION ALL
      SELECT 2 as EmpId FROM sysibm.sysdummy1 UNION ALL
      SELECT 3 as EmpId FROM sysibm.sysdummy1 UNION ALL
      SELECT 4 as EmpId FROM sysibm.sysdummy1 UNION ALL
      SELECT 5 as EmpId FROM sysibm.sysdummy1
     ) el LEFT JOIN
     Employee e
     ON el.EmpId = e.EmpId LEFT JOIN
     Address a 
     ON el.EmpId = a.EmpId LEFT JOIN
     Organization o
     ON el.EmpId = o.EmpId ;

或使用方便的快捷方式：

SELECT e.EmpName, el.EmpId, a.Address, o.OrgCode
FROM (VALUES (1), (2), (3), (4), (5)) el(EmpId)
     Employee e
     ON el.EmpId = e.EmpId LEFT JOIN
     Address a 
     ON el.EmpId = a.EmpId LEFT JOIN
     Organization o
     ON el.EmpId = o.EmpId ;

Answer 2

通过更新，它仍然是左连接：

SELECT t.EmpId, NVL(A.EmpName, 'N/A'), NVL(B.Address, 'N/A'), 
       NVL(C.OrgCode, 'N/A')
FROM TABLE(VALUES ('1'), ('2'), ('3'), ('4'), ('5')) AS t(empid)
    LEFT OUTER JOIN Employee A
        ON t.empid = A.empid
    LEFT OUTER JOIN Address B 
        ON t.EmpId = B.EmpId 
    LEFT OUTER JOIN Organization C 
        ON t.EmpId = C.EmpId
;

作为一个注释，通过将数字放在引号中，您将它们变成一个字符串。如果EmpId是一个字符串，这很好，但如果它是一个数字，那么它的效率会降低。

Answer 3

尝试使用LEFT JOIN代替：

SELECT A.EmpName, A.EmpId,B.Address, C.OrgCode
FROM Employee A
    left join Address B on A.EmpId = B.EmpId 
    left join Organization C on A.EmpId = C.EmpId
where A.EmpId in ('1', '2', '3', '4', '5');

如果IN子句中没有行，则返回虚拟值

3 个答案: