1. 初始化表结构

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;-- ----------------------------
-- Table structure for t_city
-- ----------------------------
DROP TABLE IF EXISTS `t_city`;
CREATE TABLE `t_city`  (`id` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,`code` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,`city` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;-- ----------------------------
-- Table structure for t_shool
-- ----------------------------
DROP TABLE IF EXISTS `t_shool`;
CREATE TABLE `t_shool`  (`id` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL,`city_code` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,`school` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;SET FOREIGN_KEY_CHECKS = 1;

INSERT INTO `t_city` (`id`, `code`, `city`) VALUES ('1', 'A', '北京');
INSERT INTO `t_city` (`id`, `code`, `city`) VALUES ('2', 'B', '上海');
INSERT INTO `t_city` (`id`, `code`, `city`) VALUES ('3', 'C', '成都');
INSERT INTO `t_city` (`id`, `code`, `city`) VALUES ('4', 'D', '重庆');INSERT INTO `t_shool` (`id`, `city_code`, `school`) VALUES ('1', 'A', '北京大学');
INSERT INTO `t_shool` (`id`, `city_code`, `school`) VALUES ('2', 'B', '上海大学');
INSERT INTO `t_shool` (`id`, `city_code`, `school`) VALUES ('3', 'C', '成都大学');
INSERT INTO `t_shool` (`id`, `city_code`, `school`) VALUES ('4', 'E', '西南大学');
INSERT INTO `t_shool` (`id`, `city_code`, `school`) VALUES ('5', 'D', '重庆科技大学');
INSERT INTO `t_shool` (`id`, `city_code`, `school`) VALUES ('6', 'A', '清华大学');

innner join

---------------------INNER JOIN---------------------------
SELECT* 
FROMt_cityINNER JOIN t_shool ON ( t_city.`code` = t_shool.city_code )
WHERE 1=1	

left join

SELECT* 
FROMt_cityLEFT JOIN t_shool ON ( t_city.`code` = t_shool.city_code )
WHERE 1=1	

right join 

SELECT* 
FROMt_cityRIGHT JOIN t_shool ON ( t_city.`code` = t_shool.city_code )
WHERE 1=1