我正在研究知识产权管理系统,我在数据库中有2个表 - 商标和设计。
然后我有反对这样的事情。这意味着,如果其他人有商标或设计,看起来像我们的客户,经理可以创造新的反对意见。
例如,我有3个表:
商标:
id
name
设计
id
name
oppostion:
id
name
object_id
object_table
我不知道,反对意见与表格相关,但我应该有可能提出这样的问题:
SELECT id, name, opposition_object.name FROM opposition
LEFT JOIN (trademark|design) as opposition_object on opposition.object_id = (trademark|design).id
首先,我考虑将表名存储为对立表的object_table列,但后来我意识到我不知道是否可以查询表名,首先,它确实是一个糟糕的设计。
但是我受到了打击,没有任何想法。那么有人有任何想法如何处理它?</ p>
答案 0 :(得分:3)
也许是这样的:
SELECT
id,
name,
COALESCE(trademark.name,design.name) AS object_name
FROM
opposition
LEFT JOIN trademark
on opposition.object_id = trademark.id
AND trademark.object_table ='trademark'
LEFT JOIN design
on opposition.object_id = design.id
AND design.object_table ='design'
答案 1 :(得分:0)
SELECT opposition.id, opposition.name, trademark.name AS object_name
FROM opposition
LEFT JOIN trademark
ON opposition.object_id = trademark.id
WHERE opposition.object_table = 'trademark'
UNION
SELECT opposition.id, opposition.name, design.name AS object_name
FROM opposition
LEFT JOIN design
ON opposition.object_id = design.id
WHERE opposition.object_table = 'design'
这会发出两个查询:一个加入trademark
表,另一个加入design
。然后使用UNION
将结果统一到一个结果集中。