MySQLJOIN multi-table join (4)

In addition to two commonly used table connections, the MySQLJOIN multi-table JOIN syntax also supports multi-table JOIN. The basic syntax for multi-table JOIN is as follows:... FROMtable1INNER | LEFT | RIGHTJOINtable2ONconditionINNER | LEFT | RIGHTJOINtable3ONcondition... JOIN multi-table JOIN achieves multi-table JOIN from multiple tables

In addition to two commonly used table connections, the SQL (MySQL) JOIN syntax also supports multi-Table connections. The basic syntax for multi-table join is as follows :... FROM table1 INNER | LEFT | right join table2 ON condition INNER | LEFT | right join table3 ON condition... JOIN multi-table JOIN enables

MySQL JOIN multi-table JOIN

In addition to the two commonly used table joins, the SQL (MySQL) JOIN syntax also supports multi-Table joins. The basic syntax for multi-table join is as follows:

... FROM table1 INNER|LEFT|RIGHT JOIN table2 ON condition INNER|LEFT|RIGHT JOIN table3 ON condition ...

JOIN multi-table JOIN allows you to obtain relevant data from multiple tables. The following are three original data tables:

Articles:

Aid	Title	Content	Uid	Tid
1	Article 1	Article 1 body content...	1	1
2	Article 2	Article 2 body content...	1	2
3	Article 3	Article 3 body content...	2	1
5	Article 5	Article 5 body content...	4	1

User table:

Uid	Username	Email
1	Admin	Admin@5idev.com
2	James	Xiao@163.com
3	Jack	Jack@gmail.com

Type document type table:

Tid	Typename
1	Common articles
2	Excellent articles
3	Draft

MySQL inner join multi-table

We use inner join to list data associated with all three tables:

SELECT article.aid,article.title,user.username,type.typename FROM article INNER JOIN user ON article.uid=user.uid INNER JOIN type ON article.tid=type.tid

The returned query result is as follows:

Aid	Title	Username	Typename
1	Article 1	Admin	Common articles
2	Article 2	Admin	Excellent articles
3	Article 3	James	Common articles

MySQL left join multi-table

Use left join to query three tables:

SELECT article.aid,article.title,user.username,type.typename FROM article LEFT JOIN user ON article.uid=user.uid LEFT JOIN type ON article.tid=type.tid

The returned query result is as follows:

Aid	Title	Username	Typename
1	Article 1	Admin	Common articles
2	Article 2	Admin	Excellent articles
3	Article 3	James	Common articles
4	Article 4	NULL	Common articles

MySQL right join multi-table

Use right join to query three tables:

SELECT article.aid,article.title,user.username,type.typename FROM article RIGHT JOIN user ON article.uid=user.uid RIGHT JOIN type ON article.tid=type.tid

The returned query result is as follows:

Aid	Title	Username	Typename
1	Article 1	Admin	Common articles
2	Article 2	Admin	Excellent articles
3	Article 3	James	Common articles
NULL	NULL	NULL	Draft

It can be seen that in right join, only all data of the last right join table is listed.

Description

For MySQL multi-table JOIN, you can also mix INNER, LEFT, and RIGHT. The returned results are related to the order of keywords. If you are interested, you can test the results by yourself.

From http://www.5idev.com/p-php_mysql_join_multi_table.shtml