[MySQL] cross-database join

Objectives: A database tables in database B can join tables.

Environment: Windows system, free installation mysql-5.7.22.

Requirements: a lot of tables in a database, a table by business to a different database, save the necessary relationships between tables.

First, open the FEDERATED engine

Executive order: SHOW ENGINES;Check the mysql database Federated engine is turned on. Shown below, it is not turned on.

Modify the root folder mysql my.ini file (Linux file system modifications my.cnf): Add a new row, Federated content, as shown below:
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Restart MySQL
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Execute command again: SHOW ENGINES; you can see Federated engine is turned on.
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Second, two new databases: A and B

A library table to add a student:

CREATE TABLE student(
    id VARCHAR(10) NOT NULL DEFAULT '' COMMENT '主键id',
    student_name VARCHAR(10) DEFAULT NULL COMMENT '学生姓名',
    school_id VARCHAR(10) NOT NULL DEFAULT '' COMMENT '学校id',
    PRIMARY KEY(id) 
)ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='学生表';

B Add a school library table:

CREATE TABLE school(
    id VARCHAR(10) NOT NULL DEFAULT '' COMMENT '主键id',
    school_name VARCHAR(10) DEFAULT NULL COMMENT '学校名称',
    PRIMARY KEY(id) 
)ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='学校表';

Third, the data added to the table

A row of data is added in the database:

id = 1 
student_name = 琚建飞
school_id = 1

Adding a line of data in the database B:

id=1
school_name = 廊坊师范

Fourth, the establishment of a remote table in the database A

CREATE TABLE school (
  `id` varchar(10) NOT NULL DEFAULT '' COMMENT '主键id',
  `school_name` varchar(10) DEFAULT NULL COMMENT '学校名称',
  PRIMARY KEY (`id`)
) ENGINE=FEDERATED DEFAULT CHARSET=utf8 
    COMMENT='学校表-远程表' CONNECTION='mysql://root:root@localhost:3306/b/school';
-- root:root   远程数据库的账号和密码
-- localhost:3306  远程数据库的ip和端口
-- b  远程数据库的名称
-- school 远程数据库的表名称

Fifth, the implementation of join operations

SELECT s.id, s.student_name, sc.school_name 
FROM student s JOIN school sc ON s.school_id = sc.id

Result:

Local table and a remote table

The local table update operations, remote table will be updated simultaneously.
Delete the local table, the remote table is not deleted.
Remote table structure changes, the local table is not updated.

Original Address: https: //blog.csdn.net/gnd15732625435/article/details/80270096