两表联合查询

SQL架构

表1: Person

+-------------+---------+

| 列名         | 类型     |

+-------------+---------+

| PersonId    | int     |

| FirstName   | varchar |

| LastName    | varchar |

+-------------+---------+

PersonId 是上表主键

表2: Address

+-------------+---------+

| 列名         | 类型    |

+-------------+---------+

| AddressId   | int     |

| PersonId    | int     |

| City        | varchar |

| State       | varchar |

+-------------+---------+

AddressId 是上表主键

编写一个 SQL 查询，满足条件：无论 person 是否有地址信息，都需要基于上述两表提供 person 的以下信息：

FirstName, LastName, City, State

---

先开启本地mysql服务 

使用数据库test，新建两个表person和address，并向两数据表中添加数据

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for person
-- ----------------------------
DROP TABLE IF EXISTS `person`;
CREATE TABLE `person`  (
  `PersonId` int(11) NOT NULL,
  `FirstName` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `LastName` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`PersonId`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = latin1 COLLATE = latin1_swedish_ci ROW_FORMAT = Compact;

-- ----------------------------
-- Records of person
-- ----------------------------
INSERT INTO `person` VALUES (100001, '张', '三');
INSERT INTO `person` VALUES (100002, '李', '四');
INSERT INTO `person` VALUES (100003, '王', '五');
INSERT INTO `person` VALUES (100004, '马', '六');
INSERT INTO `person` VALUES (100005, '陈', '七');

SET FOREIGN_KEY_CHECKS = 1;

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for address
-- ----------------------------
DROP TABLE IF EXISTS `address`;
CREATE TABLE `address`  (
  `AddressId` int(11) NOT NULL,
  `PersonId` int(11) NULL DEFAULT NULL,
  `City` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `State` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`AddressId`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = latin1 COLLATE = latin1_swedish_ci ROW_FORMAT = Compact;

-- ----------------------------
-- Records of address
-- ----------------------------
INSERT INTO `address` VALUES (200001, 100003, '北京', '1');
INSERT INTO `address` VALUES (200002, 100005, '上海', '0');
INSERT INTO `address` VALUES (200003, 100002, '杭州', '1');
INSERT INTO `address` VALUES (200004, 100004, '深圳', '0');
INSERT INTO `address` VALUES (200005, 100001, '广州', '1');

SET FOREIGN_KEY_CHECKS = 1;

​题目要求：​

​编写一个 SQL 查询，满足条件：​

无论 person 是否有地址信息，

都需要基于上述两表提供 person 的以下信息：FirstName, LastName, City, State

---

SELECT
  FirstName,
  LastName,
  City,
  State 
FROM
  person p
  LEFT JOIN address a ON p.PersonId = a.PersonId

---

SELECT
  FirstName,
  LastName,
  City,
  State 
FROM
  person p
  INNER JOIN address a ON p.PersonId = a.PersonId

---

SELECT
  FirstName,
  LastName,
  City,
  State 
FROM
  person p
  RIGHT JOIN address a ON p.PersonId = a.PersonId

 

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1. 1. 
      
2. ​INNER JOIN：内连接，如果表中有至少一个匹配，则返回行
3. ​LEFT JOIN：左连接，即使右表中没有匹配，也从左表返回所有的行
4. ​RIGHT JOIN：右连接，即使左表中没有匹配，也从右表返回所有的行
   1.