是否可以使用 CASE 语句从一张表中列出所有可能的用户角色？ [Teradata]

Question

我正在弄清楚是否可以列出用户需要拥有的所有 4 个角色，每个角色都带有“是”或“否”声明。例如。

SELECT DISTINCT Grantee, GranteeKind, RoleName, WhenGranted,
    CASE
        WHEN RoleName='Manager' THEN 'Yes'
        WHEN RoleName='Assistant' THEN 'Yes'
        WHEN RoleName='Executive' THEN 'Yes'
        WHEN RoleName='Deputy' THEN 'Yes'
                    ELSE NULL
            END AS "Already granted?"
    FROM DBC.RolesM
    WHERE Grantee='UserName' 
    AND RoleName IN
    ('Manager',
    'Assistant',
    'Executive',
    'Deputy');

我的查询获取以下结果，它是 100% 正确的。

Grantee    GranteeKind  RoleName    WhenGranted Already Granted? 
UserName    User    Manager         2018-01-30        Yes
UserName    User    Assistant       2016-01-30        Yes

不过，我想知道是否有可能得到这样的东西，所以我们对未分配的角色有明确的答案。

Grantee    GranteeKind  RoleName    WhenGranted Already Granted? 
UserName    User    Manager         2018-01-30        Yes
UserName    User    Assistant       2016-01-30        Yes
UserName    User    Executive       2016-01-30        No
UserName    User    Deputy          2016-01-30        No

Answer 1

使用cross join 生成行，然后使用left join 引入值。

不幸的是，Teradata 使生成角色列表有点困难，但这应该可以：

select g.Grantee, g.GranteeKind, r.RoleName, 
       rm.WhenGranted,
       (case when rm.RoleName is not null then 'Yes' else 'No' end) as already_granted
from (select distinct grantee, GranteeKind
      from DBC.RolesM
     ) g cross join
     (select distinct RoleName
      from DBC.RolesM
      where RoleName in ('Manager', 'Assistant', 'Executive', 'Deputy')
     ) r left join
     DBC.RolesM rm
     on rm.grantee = g.grantee and rm.rolename = r.rolename

Answer 2

尝试下面给出的查询，希望对您有所帮助。

SELECT  *
FROM    ( SELECT  Grantee, GranteeKind, RoleName, WhenGranted, ROW_NUMBER() OVER (PARTITION BY RoleName ORDER BY id) AS RowNumber
    CASE
        WHEN RoleName='Manager' THEN 'Yes'
        WHEN RoleName='Assistant' THEN 'Yes'
        WHEN RoleName='Executive' THEN 'Yes'
        WHEN RoleName='Deputy' THEN 'Yes'
                    ELSE NULL
            END AS "Already granted?"
    FROM DBC.RolesM
    WHERE Grantee='UserName' 
    AND RoleName IN
    ('Manager',
    'Assistant',
    'Executive',
    'Deputy')) AS a
WHERE   a.RowNumber = 1

Answer 3

我现在无法访问我的 TD，所以我是凭记忆这样做的：

select Grantee, GranteeKind, RoleName,
    max(managerRole), max(AssistantRole), max(ExecutiveRole), max(DeputyRole)
from (
  SELECT DISTINCT Grantee, GranteeKind, RoleName, WhenGranted,
    CASE
        WHEN RoleName='Manager' THEN 'Yes' ELSE 'No'
    END as ManagerRole,
    CASE
        WHEN RoleName='Assistant' THEN 'Yes' ELSE 'No'
    END as AssistantRole,
    CASE
        WHEN RoleName='Executive' THEN 'Yes' ELSE 'No'
    END as ExecutiveRole,
    CASE
        WHEN RoleName='Deputy' THEN 'Yes' ELSE 'No'
    END AS DeputyRole
  FROM DBC.RolesM
  WHERE Grantee='UserName' 
    AND RoleName IN
    ('Manager',
    'Assistant',
    'Executive',
    'Deputy')
  ) as DT
group by 1, 2, 3
order by 1, 2;

希望不会有语法错误。

基本上内部查询会产生一个这样的列表：

Grantee etc, ManagerRole, AssistantRole, etc
abc,             Yes          No
abc,             No           Yes
def,             Yes          No
def,             No           No

然后外部查询选择每一列的聚合。我们正在做一个最大值，所以“是”将击败“否”。如果用户没有该角色，您只会收到否。

注意：假设 Grantee、GrantKind 和 RoleName 都相同。如果不是，您将获得每个受赠人的多条记录。我不得不省略“授予时”，因为那可能是在不同的时间。