在 php-mysql 中加入 2 个或更多表

Question

I want to join 2 or more table in my Hotel management project, so what all are the steps to join tables? Is it necessary to give foreign key in each table we need to join or works without foreign key?

Answer 1

The steps are:

1. Write a JOIN query. You're done!

You can JOIN using columns that are neither a primary key nor foreign key. Eg,

select *
from (select 'x' as a) t1
inner join (select 'x' as a) t2 on t1.a = t2.a

A query has a JOIN clause and an ON clause. The JOIN clause says what type of JOIN it is and which tables are being JOIN ed. The ON clause specifies which columns to JOIN on.

Answer 2

No you don't need to use foreign keys specifically, although you will probably use an equivalent. (note, the default engine MyISAM, does not support foreign keys, if you want to use them, use InnoDB or $otherEngine).

For joins I would suggest reading the documentation on joins .

Answer 3

Simple join, without redundant ID output:

SELECT * FROM foo JOIN bar USING (id);

Assuming the id column is defined in both tables as primary, hence creating the relationship between tables you want to join.

However, there are different type of joins (natural, straight, left, right), based on what criteria and requirements you have. Check out the MySQL API manual, it will provide you with sufficient information.

Answer 4

我认为对于您的情况（如顶部帖子中所述），创建一个 PHP 文件来分别获取每个表的来宾数据会更有意义，至少对我而言，将 6 个表连接在一起似乎是太麻烦，而且在实际中不是很有效。