实例使用数据集：

SET NAMES utf8mb4;

SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------

-- Table structure for student

-- ----------------------------

DROP TABLE IF EXISTS `student`;

CREATE TABLE `student`  (

  `id` int(11) NOT NULL,

  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

  `age` int(11) NULL DEFAULT NULL,

  `addr` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

  PRIMARY KEY (`id`) USING BTREE

) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------

-- Records of student

-- ----------------------------

INSERT INTO `student` VALUES (1, '张三', 16, '北京市通州区');

INSERT INTO `student` VALUES (2, '李四', 17, '河北石家庄');

INSERT INTO `student` VALUES (3, '李师师', 17, '河南洛阳');

INSERT INTO `student` VALUES (4, '杜甫', 18, '陕西西安');

INSERT INTO `student` VALUES (5, '高适', 16, '安徽福州');

INSERT INTO `student` VALUES (11, '李白', 11, '河北张家口');

SET FOREIGN_KEY_CHECKS = 1;

SET NAMES utf8mb4;

SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------

-- Table structure for core

-- ----------------------------

DROP TABLE IF EXISTS `core`;

CREATE TABLE `core`  (

  `id` int(11) NOT NULL,

  `sid` int(11) NULL DEFAULT NULL,

  `cname` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

  `core` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

  PRIMARY KEY (`id`) USING BTREE

) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------

-- Records of core

-- ----------------------------

INSERT INTO `core` VALUES (1, 1, '数学', '98');

INSERT INTO `core` VALUES (2, 1, '语文', '87');

INSERT INTO `core` VALUES (3, 1, '英语', '76');

INSERT INTO `core` VALUES (4, 2, '数学', '96');

INSERT INTO `core` VALUES (5, 2, '语文', '92');

INSERT INTO `core` VALUES (6, 2, '英语', '81');

INSERT INTO `core` VALUES (7, 3, '数学', '45');

INSERT INTO `core` VALUES (8, 3, '语文', '76');

INSERT INTO `core` VALUES (9, 7, '英语', '45');

INSERT INTO `core` VALUES (19, 8, '数学', '87');

SET FOREIGN_KEY_CHECKS = 1;

student表，单表数据情况：select * from student s

core表，单标数据查询情况：SELECT * FROM `core` c

多表，内连接：select s.*,c.* from student s inner join `core` c on s.id = c.sid

左连接效果：

select s.*,c.* from student s left join `core` c on s.id = c.sid

有链接：select s.*,c.* from student s right join `core` c on s.id = c.sid

/*左外连接、右外连接跟左连接、右连接的结果一样*/select s.*,c.* from student s left OUTER JOIN `core` c on s.id = c.sidselect s.*,c.* from student s right outer join `core` c on s.id = c.sid