无法计算为什么子查询返回多于一行

我有以下数据也在SQL FIDDLE。无法计算为什么子查询返回多于一行

CREATE TABLE completework 
    (`id` int, `workerid` int, `checkerid` int); 

    CREATE TABLE worker 
    (`id` int, `name` varchar(20)); 

    INSERT INTO completework 
     (`id`, `workerid`, `checkerid`) 
    VALUES 
     (1, 2, 4), 
     (2, 3, 5), 
     (3, 4, 1), 
     (4, 5, 2), 
     (5, 1, 3), 
     (6, 2, 4), 
     (7, 3, 5), 
     (8, 4, 1), 
     (9, 5, 2), 
     (10, 1, 3), 
     (11, 2, 4), 
     (12, 3, 5), 
     (13, 4, 1), 
     (14, 5, 2); 

    INSERT INTO worker 
     (`id`, `name`) 
    VALUES 
    (1, 'Anthony'), 
    (2, 'Bill'), 
    (3, 'Claire'), 
    (4, 'Daniel'), 
    (5, 'Emma');

我想返回结果当操作员或者是工人或检查，所以我想我需要工会的两列，但是当我尝试这样做，我得到了错误

Subquery returns more than 1 row

我曾尝试以下

select 
    workerid as wid, 
    wn.name 
    from completework 
    inner join worker wn on completework.workerid=wn.id 
    group by wid

以上只是得到workerid列

select 
    checkerid as cid, 
    wn.name 
    from completework 
    inner join worker wn on completework.checkerid=wn.id 
    group by cid

以上只是得到checkerid列

SELECT DISTINCT workedonid FROM (
     SELECT checkerid workedonid FROM completework 
     UNION 
     SELECT workerid workedonid FROM completework 
    )c 
    ORDER BY workedonid ASC

以上从任一列

select 
     (
      SELECT DISTINCT workedonid FROM (
       SELECT checkerid workedonid FROM completework 
       UNION 
       SELECT workerid workedonid FROM completework 
      )c 
     ) a, 
    wn.name 
    from completework 
    inner join worker wn on completework.checkerid=wn.id 
    group by a

获得一个ID在上面，我想上述工作为子查询，但我得到的错误，我该如何解决这个问题？

来源

2014-01-27 ak85

试试这个：

SELECT DISTINCT w.id AS wid, w.name 
FROM worker w 
INNER JOIN completework cw ON w.id IN (cw.workerid, cw.checkerid);

入住这SQL FIDDLE DEMO

输出

| WID | NAME | 
|-----|---------| 
| 2 | Bill | 
| 4 | Daniel | 
| 3 | Claire | 
| 5 | Emma | 
| 1 | Anthony |

来源

2014-01-27 04:44:05

无法计算为什么子查询返回多于一行

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