MySQL数据库设计性能和查询

Question

MySQL DB设计架构

嗨，正如您所看到的，这里有2种设计。 两者都基于每个主表只有一行，而其他关系表中只有主表行。 [1：1]

设计1：有可为空的表外键； 电源表中的项目，其他，秒

设计2：其他人都有主表的外键

我的问题是，哪种设计合适？ 为了进行Select SQL查询，在“设计1”中需要使用UNION，而对于“设计2”，我想选择LEFT JOIN。 那么，就通过大量数据的性能而言，合适的方法和sql查询应该如何？

更新 ：

SELECT mains.id as mainId, items.id as id, mains.title as title, items.name as name
    FROM items, mains where mains.itemId=items.id
UNION
SELECT mains.id as mainId, others.id as id, mains.title as title, others.name as name
    FROM others, mains where mains.otherId=others.id  
UNION
SELECT mains.id as mainId, seconds.id as id, mains.title as title, seconds.name as name
    FROM seconds, mains where mains.secondId=seconds.id

------------------------------

SELECT  *
    FROM  mains
    LEFT JOIN  items ON mains.itemId=items.Id
    LEFT JOIN  seconds ON mains.secondId=seconds.id
    LEFT JOIN  others ON mains.otherId=others.id 

------------------------------

SELECT main.id as mainId, item.id as id, main.title as title, item.name as name
    FROM item, main where main.id=item.mainId
UNION
SELECT main.id as mainId, other.id as id, main.title as title, other.name as name
    FROM other, main where main.id=other.mainId  
UNION
SELECT main.id as mainId, second.id as id, main.title as title, second.name as name
    FROM second, main where main.id=second.mainId

-------------------------------

SELECT  *
    FROM  mains
    LEFT JOIN  items ON mains.itemId=items.Id
    LEFT JOIN  seconds ON mains.secondId=seconds.id
    LEFT JOIN  others ON mains.otherId=others.id 

不同的SQL查询方法..！ 哪一个？ 性能？

Answer 1

如果主表中的每个记录与项具有一对一的关系，那么我更喜欢将其他表和第二个表全部存储在一个表中，而不必使用JOIN或UNION。