Mysql数据库演示内连接、左连接、右连接

前提

建了两个表：student,worker。

CREATE TABLE
IF NOT EXISTS student (
    student_id INT (11) NOT NULL AUTO_INCREMENT,
    student_name VARCHAR (16) NOT NULL,
    PRIMARY KEY (student_id)
) ENGINE = INNODB DEFAULT CHARSET = utf8;

CREATE TABLE
IF NOT EXISTS worker (
    worker_id INT (11) NOT NULL AUTO_INCREMENT,
    worker_name VARCHAR (16) NOT NULL,
    PRIMARY KEY (worker_id)
) ENGINE = INNODB;

插入数据：

INSERT INTO student (student_id, student_name)
VALUES
    (1, 'one'),
    (2, 'two'),
    (3, 'three'),
    (4, 'four'),
    (5, 'A');

INSERT INTO worker (worker_id, worker_name)
VALUES
    (1, 'one'),
    (2, 'two'),
    (3, 'A'),
    (4, 'B');

三种连接

内连接：

SELECT
    *
FROM
    student s
INNER JOIN worker w ON s.student_name = w.worker_name;

结果：

左连接：

SELECT
    *
FROM
    student s
LEFT JOIN worker w ON s.student_name = w.worker_name;

结果：

右连接：

SELECT
    *
FROM
    student s
RIGHT JOIN worker w ON s.student_name = w.worker_name;

结果：

结论

这三种连接就类似于下图：