从不同的列加入同一张表上的多个计数？

Question

我觉得这应该很容易，但为时已晚，我正在苦苦挣扎。

假设（在 oracle 12 db 中）我有一个表格，它表示在不同的事件中哪些员工在酒吧担任什么角色，如下所示：

+----------+----------+-------+------------+----------+
| event_id | bar      | doors | cloak_room | keg_room |
+----------+----------+-------+------------+----------+
| 2        | bob      | bill  | john       | mary     |
+----------+----------+-------+------------+----------+
| 3        | bob      | bill  | mary       | kev      |
+----------+----------+-------+------------+----------+
| 4        | bob      | john  | louise     | mary     |
+----------+----------+-------+------------+----------+
| 5        | kyle     | kev   | sarah      | louise   |
+----------+----------+-------+------------+----------+
| 6        | jennifer | bob   | jay        | john     |
+----------+----------+-------+------------+----------+
| 7        | john     | bill  | mary       | steve    |
+----------+----------+-------+------------+----------+ 

我想统计一下每位员工参与了多少活动，如下所示：

+-------+--------+
| count | person |
+-------+--------+
| 4     | bob    |
+-------+--------+
| 4     | john   |
+-------+--------+
| 3     | bill   |
+-------+--------+
| 3     | mary   |
+-------+--------+
| 2     | kev    |
+-------+--------+
| 2     | louise |
+-------+--------+
| 1     | jay    |
+-------+--------+
| 1     | steve  |
+-------+--------+ 

我们在这里看到 bob 的计数为 4 - 因为他与 4 个不同的 event_id 相关联：3 作为酒保，1 作为门卫。

（假设没有两个员工同名，也没有人可以同时做两份工作）

我该怎么做？

对于一个“角色”来说很明确：

select count(event_id), bar group by bar

但是是否有一种优雅的方法可以对所有列执行此操作 - 无需完全连接和字符串连接？

谢谢！

Answer 1

您应该更改数据的结构，以便每个事件/人员/角色有一行。然后你可以只使用聚合。

您也可以在查询中这样做：

select who, count(*)
from (select event_id, 'bar' as job, bar as who from t union all
      select event_id, 'doors' as job, doors as who from t union all
      select event_id, 'cloak_room' as job, cloak_room as who from t union all
      select event_id, 'keg_room' as job, keg_room as who from t
     ) jw
group by who;

如果某人可以在一个活动中拥有多项工作，请使用count(distinct event_id)。

编辑：

我看到您使用的是 Oracle 12c。然后使用横向连接/交叉应用：

select who, count(*)
from t cross apply
     (select t.event_id, 'bar' as job, t.bar as who from dual union all
      select t.event_id, 'doors' as job, t.doors as who from dual from dual union all
      select event_id, 'cloak_room' as job, cloak_room as who from dual union all
      select t.event_id, 'keg_room' as job, t.keg_room as who from dual
     ) jw
group by who;

Answer 2

您可以在嵌套的内部查询中按字符串列计数，然后按照您想要的顺序将它们向上 在外面 em>：

SELECT sum(count) count, person
  FROM
(
 SELECT count(event_id) count, bar person FROM mytable GROUP BY bar UNION ALL
 --> P.S. Only aliasing as "person" is enough in this upper "select" for all 
 --> four "select" statements inside the parentheses.
 SELECT count(event_id)      , doors      FROM mytable GROUP BY doors UNION ALL
 SELECT count(event_id)      , cloak_room FROM mytable GROUP BY cloak_room UNION ALL
 SELECT count(event_id)      , keg_room   FROM mytable GROUP BY keg_room
)
GROUP BY person
ORDER BY 1 desc, 2;

COUNT   PERSON
   4    bob
   4    john
   3    bill
   3    mary
   2    kev
   2    louise
   1    jay
   1    jennifer
   1    kyle
   1    mary2
   1    sarah
   1    steve

SQL Fiddle Demo