在 Java 中，多个 select 查询或连接，哪一个是更好的做法？

Question

I have five tables in MySQL database, each of them has the one-to-one relationship with the User table that stores the username and password, there is a user_id field in User table as the foreign key for all the other tables.

If I need to implement a "Login" function with Java, to get all data of a certain user from all these five tables, would it be a good practice to use JOIN to query these five tables at once?

I also have another question, would it be a better choice to combine these five tables together as one single table as they have one-to-one relationship?

Answer 1

As general principle, 1 to 1 relationships should be in the same table.

Exceptions can include:

• privilege separation - mysql users have different table level access.
• locking separation, one table as a particularly high updated field than for a userid that needs to be separate from another table of high userid updates.
• performance - row size - one table has large number of columns that isn't frequently needed, so keep it out of the innodb buffer pool by keeping those columns in a different table.

Answer 2

Idea behind creating multiple tables with foreign key reference is to support one-to-many relationship. Since your table data has one-to-one relationship, there is no point creating multiple table if number of columns including all tables, having one-to-one relationship, is less than Mysql table column count limit.

Incase your business requirement doesn't allow to change the current schema, you can go for join to get all the data in single network call rather than making multiple network call to get data as network call latency is not predictable.