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Multi-table query
Create several tables with relationships between them.
user table
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for sys_admin
-- ----------------------------
DROP TABLE IF EXISTS `sys_admin`;
CREATE TABLE `sys_admin` (
`user_id` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '登录账号',
`password` varchar(100) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '登录密码',
`datetime` datetime(0) NULL DEFAULT NULL COMMENT '添加时间\r\n',
`username` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '管理员姓名',
`salt` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '盐',
PRIMARY KEY (`user_id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;
-- ----------------------------
-- Records of sys_admin
-- ----------------------------
INSERT INTO `sys_admin` VALUES ('123456', 'be5b9922e3392dc42153f9c9870b7e78', '2022-06-05 12:12:59', '三禾', 'Idq29*0uAY');
INSERT INTO `sys_admin` VALUES ('263561', '8df16f91f1139510d0266791ce78acde', '2022-05-31 23:26:52', '胡歌', 'Qa#8uA!KwC');
INSERT INTO `sys_admin` VALUES ('茶凡', 'c7e9768beca397fb4db195b2204b01ec', '2022-06-08 20:33:44', 'Matrix', 'KmXcY)jNOO');
SET FOREIGN_KEY_CHECKS = 1;
User role table
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for t_user_role
-- ----------------------------
DROP TABLE IF EXISTS `t_user_role`;
CREATE TABLE `t_user_role` (
`id` int(6) NOT NULL,
`userid` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
`roleid` int(6) NULL DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;
-- ----------------------------
-- Records of t_user_role
-- ----------------------------
INSERT INTO `t_user_role` VALUES (1, '263561', 1);
INSERT INTO `t_user_role` VALUES (2, '123456', 2);
INSERT INTO `t_user_role` VALUES (3, '茶凡', 1);
SET FOREIGN_KEY_CHECKS = 1;
character sheet
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for t_role
-- ----------------------------
DROP TABLE IF EXISTS `t_role`;
CREATE TABLE `t_role` (
`id` int(6) NOT NULL AUTO_INCREMENT,
`name` varchar(60) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;
-- ----------------------------
-- Records of t_role
-- ----------------------------
INSERT INTO `t_role` VALUES (1, 'admin');
INSERT INTO `t_role` VALUES (2, 'user');
INSERT INTO `t_role` VALUES (3, 'product');
SET FOREIGN_KEY_CHECKS = 1;
Permissions table
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for t_perms
-- ----------------------------
DROP TABLE IF EXISTS `t_perms`;
CREATE TABLE `t_perms` (
`id` int(6) NOT NULL AUTO_INCREMENT,
`name` varchar(80) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
`url` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;
-- ----------------------------
-- Records of t_perms
-- ----------------------------
INSERT INTO `t_perms` VALUES (1, 'user:*:*', NULL);
INSERT INTO `t_perms` VALUES (2, 'product:*:01', NULL);
INSERT INTO `t_perms` VALUES (3, 'order:*:*', NULL);
SET FOREIGN_KEY_CHECKS = 1;
Role permission table
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for t_role_perms
-- ----------------------------
DROP TABLE IF EXISTS `t_role_perms`;
CREATE TABLE `t_role_perms` (
`id` int(6) NOT NULL,
`roleid` int(6) NULL DEFAULT NULL,
`permsid` int(6) NULL DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;
-- ----------------------------
-- Records of t_role_perms
-- ----------------------------
INSERT INTO `t_role_perms` VALUES (1, 1, 1);
INSERT INTO `t_role_perms` VALUES (2, 1, 2);
INSERT INTO `t_role_perms` VALUES (3, 2, 1);
INSERT INTO `t_role_perms` VALUES (4, 3, 2);
INSERT INTO `t_role_perms` VALUES (5, 1, 3);
SET FOREIGN_KEY_CHECKS = 1;
relationship between tables
MySQL connection
Use joins to query data from multiple tables.
SELECT table1.COLUMN, table2.COLUMN FROM table1, table2 WHERE table1.column1 = table2.column2;
Write the join condition in the WHERE clause.
When there are identical columns in the table, add the table name prefix before the column name.
Related query user table and user role table
SELECT s.user_id,s.username,t.roleid FROM `sys_admin` s,t_user_role t WHERE s.user_id = t.userid;
--------------------------------------------------
结果：
123456 三禾 2
15681026356 胡歌 1
茶凡 Matrix 1
--------------------------------------------------
Related query user table, user role table and role table
SELECT
s.user_id,
s.username,
tur.roleid,
tr.name
FROM
`sys_admin` s
JOIN t_user_role tur ON s.user_id = tur.userid
JOIN t_role tr ON tur.roleid = tr.id;
--------------------------------------------------
结果：
15681026356 胡歌 1 admin
茶凡 Matrix 1 admin
123456 三禾 2 user
--------------------------------------------------
Multiple table join
To join n tables, at least n-1 join conditions are required. For example: to join three tables, at least two join conditions are required.
Cartesian set
When two tables are associated, the columns of the left table and the columns of the right table are expressed in the form of Cartesian product.
outer join
Left outer join: left join
When two tables are related, all the left table is retained. If the right table cannot be related, null is used to indicate it.
select * from t1 left join t2 on t1.id = t2.id
Right outer join: right join
When two tables are related, the right table is retained entirely. If the left table is not related, null is used to indicate it.
select * from t1 right join t2 on t1.id = t2.id
Inner join: inner join
The two tables are associated and the intersection records in the two tables are retained.
select * from t1 inner join t2 on t1.id = t2.id;
Other connections
Blog reference (3 messages) MySQL table connection method_Zhayi's blog-CSDN blog_mysql table connection method
Blog reference: Shang Silicon Valley mysql tutorial