Question

除了此CASE语句中概述的条件外，查询还返回NULL值。我尝试在CASE中插入IS NOT NULL，但不断收到与关键字相关的错误。我很感激你的帮助。 Oracle SQL：

  SELECT DISTINCT A.DEPTID,
  CASE

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
                   WHERE A.DEPTID = B.DEPTID
                     AND B.ROLENAME = 'Employee 1')
  THEN 'Employee 1'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
                   WHERE A.DEPTID = B.DEPTID
                     AND B.ROLENAME = 'Employee 2')
  THEN 'Employee 2'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
                   WHERE A.DEPTID = B.DEPTID
                     AND B.ROLENAME = 'Manager 1')
  THEN 'Manager 1'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
                   WHERE A.DEPTID = B.DEPTID
                     AND B.ROLENAME = 'Manager 2')
  THEN 'Manager 2'

  END AS MISSING_JOBTYPE
FROM MYTABLE A

Answer 1

您似乎希望部门缺少员工类别。我会使用条件聚合和having子句：

select deptid,
       sum(case when rolename = 'Employee 1' then 1 else 0 end) as nume1,
       sum(case when rolename = 'Employee 2' then 1 else 0 end) as nume2,
       sum(case when rolename = 'Manager 1' then 1 else 0 end) as numm1,
       sum(case when rolename = 'Manager 2' then 1 else 0 end) as numm2
from mytable a
group by deptid
having nume1 = 0 or nume2 = 0 or numm1 = 0 or numm2 = 0;

这将使所有部门至少缺少这些员工角色中的一个。请注意，某些数据库不支持having子句中的别名，因此您必须重复定义表达式或使用子查询。

Answer 2

你有两种抑制空值的方法，一种是简短的：

SELECT DISTINCT A.DEPTID,
  CASE

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Employee 1')
  THEN 'Employee 1'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Employee 2')
  THEN 'Employee 2'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Manager 1')
  THEN 'Manager 1'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Manager 2')
  THEN 'Manager 2'

    ELSE 'Once upon a time NULL used to live here...'
  END AS MISSING_JOBTYPE
FROM MYTABLE A

另一个很长：

SELECT DISTINCT A.DEPTID,
  CASE

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Employee 1')
  THEN 'Employee 1'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Employee 2')
  THEN 'Employee 2'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Manager 1')
  THEN 'Manager 1'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Manager 2')
  THEN 'Manager 2'

  END AS MISSING_JOBTYPE
FROM MYTABLE A
WHERE CASE

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Employee 1')
  THEN 'Employee 1'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Employee 2')
  THEN 'Employee 2'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Manager 1')
  THEN 'Manager 1'

  WHEN NOT EXISTS (SELECT B.* FROM MYTABLE B
               WHERE A.DEPTID = B.DEPTID
                 AND B.ROLENAME = 'Manager 2')
  THEN 'Manager 2'

  END IS NOT NULL

如何向CASE添加IS NOT NULL

2 个答案: