如何从现有数据创建新的逗号分隔列? [英] How to create new comma-separated column from existing data?

问题描述

我们有以下 account 表(MySQL RDBMS):

We have the following account table (MySQL RDBMS):

+----+-------------------+----------------+-----------------+-----------------+
| id |     username      | admin_for_blog | editor_for_blog | author_for_blog |
+----+-------------------+----------------+-----------------+-----------------+
|  1 | author_only       | NULL           | NULL            | 1               |
|  2 | editor_and_author | NULL           | 2               | 2               |
|  3 | admin_only        | 3              | NULL            | NULL            |
+----+-------------------+----------------+-----------------+-----------------+

我们正在迁移到基于角色的授权，因此我们需要为上述现有数据找到新的角色.角色是:AUTHOR、EDITOR 和 ADMIN.一个用户可以链接到多个角色.角色将存储为逗号分隔值(顺序无关紧要).在上面的数据中，输出应该是:

We are migrating to a role-based authorization, so we need to find the new roles for the above existing data. Roles are: AUTHOR, EDITOR and ADMIN. A user can be linked to multiple roles. Roles will be stored as comma-separated values (order doesn't matter). In the above data, the output should then be:

+----+-------------------+---------------+----------------+-----------------+-----------------+
| id |     username      | roles         | admin_for_blog | editor_for_blog | author_for_blog |
+----+-------------------+---------------+----------------+-----------------+-----------------+
|  1 | author_only       | AUTHOR        | NULL           | NULL            | 1               |
|  2 | editor_and_author | AUTHOR,EDITOR | NULL           | 2               | 2               |
|  3 | admin_only        | ADMIN         | 3              | NULL            | NULL            |
+----+-------------------+---------------+----------------+-----------------+-----------------+

所以基本上:

• 如果author_for_blog 不为空，则添加角色AUTHOR
• 如果editor_for_blog不为空，则添加角色EDITOR
• 如果admin_for_blog 不为空，则添加角色ADMIN

• if author_for_blog is not null, then add role AUTHOR
• if editor_for_blog is not null, then add role EDITOR
• if admin_for_blog is not null, then add role ADMIN

关于如何做到这一点的任何提示?我已经能够为每个用户附加一个角色，但我找不到一种方法来管理以逗号分隔的多个角色:

Any hint on how to to this? I've been able to attach one role per user, but I can't find a way to manage multiple roles separated by commas:

select username,
    case admin_for_blog is not null when true then 'ADMIN' else
    case editor_for_blog is not null when true then 'EDITOR' else
    case author_for_blog is not null when true then 'AUTHOR' else
    'error!' end end end
from account

推荐答案

您可以使用函数 concat_ws 跳过 null 值.

You can use the function concat_ws which skips the null values.

select username,
concat_ws(','
         ,case when admin_for_blog is not null then 'ADMIN' end
         ,case when editor_for_blog is not null then 'EDITOR' end
         ,case when author_for_blog is not null then 'AUTHOR' end
         )
from account

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