MySQL:使用一个查找表查询具有不同查找ID的两个字段

Question

如果第二个 lookup.id 已被使用，我如何改进现有查询以显示正确的查找值。如果我使用派生表会更好吗？子查询？有人可以教我吗？

问题:

RECORDS TYPE    TYPE_DESC   PROCESS_ID  STATUS  QUEUE_DESC
1       1       Queued      55          4       Queued
1       2       Cancelled   84          7       Cancelled

我的目标:

RECORDS TYPE    TYPE_DESC   PROCESS_ID  STATUS  QUEUE_DESC
1       1       Initial     55          4       Queued
1       2       Follow Up   84          7       Cancelled

现有查询:

SELECT 
    COUNT(q.id) as records,
    q.type,
    l.description AS type_desc,
    q.process_id,
    q.status,
    l.description AS queue_desc
FROM
    queues q,
    lookups l
WHERE
    l.id = q.status
GROUP BY q.status;

为了更好地理解我的问题，请参阅 sqlfiddle 条目: http://sqlfiddle.com/#!2/6b7d10/6

谢谢

Answer 1

您必须加入“查找”表两次。

SELECT COUNT(q.id)    AS records
      ,q.type
      ,l1.description AS type_desc
      ,q.process_id
      ,q.status
      ,l2.description AS queue_desc
FROM queues  q
    ,lookups l1
    ,lookups l2
WHERE l1.id = q.type
  and l2.id = q.status
GROUP BY q.status;

就是这样。