mysql学习之join用法

转载  一张图看懂 SQL 的各种 join 用法

一、JOIN 使用介绍

下面例子使用的数据表如下：

-- ----------------------------
-- Table structure for dancing_hobby
-- ----------------------------
DROP TABLE IF EXISTS `dancing_hobby`;
CREATE TABLE `dancing_hobby`  (
  `id` int(11) NOT NULL COMMENT '主键',
  `stu_num` int(11) NULL DEFAULT NULL COMMENT '学号',
  `name` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '姓名',
  `age` varchar(3) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '年龄',
  `sex` varchar(2) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '男生1 女生2',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of dancing_hobby
-- ----------------------------
INSERT INTO `dancing_hobby` VALUES (1, 1001, '小红', '18', '1');
INSERT INTO `dancing_hobby` VALUES (2, 1002, '小红', '18', '2');
INSERT INTO `dancing_hobby` VALUES (3, 1003, '小黑', '18', '1');
INSERT INTO `dancing_hobby` VALUES (4, 2001, '大绿', '18', '1');
INSERT INTO `dancing_hobby` VALUES (5, 1005, '小紫', '18', '2');
INSERT INTO `dancing_hobby` VALUES (6, 2002, '大蓝', '18', '1');
INSERT INTO `dancing_hobby` VALUES (7, 1007, '小黄', '18', '1');
INSERT INTO `dancing_hobby` VALUES (8, 2003, '大白', '18', '1');
INSERT INTO `dancing_hobby` VALUES (9, 1009, '小橙', '18', '2');
INSERT INTO `dancing_hobby` VALUES (10, 2004, '大青', '18', '2');


-- ----------------------------
-- Table structure for sing_hobby
-- ----------------------------
DROP TABLE IF EXISTS `sing_hobby`;
CREATE TABLE `sing_hobby`  (
  `id` int(11) NOT NULL COMMENT '主键',
  `stu_num` int(11) NULL DEFAULT NULL COMMENT '学号',
  `name` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '姓名',
  `age` varchar(3) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '年龄',
  `sex` varchar(2) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '男生1 女生2',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of sing_hobby
-- ----------------------------
INSERT INTO `sing_hobby` VALUES (1, 1001, '小红', '18', '1');
INSERT INTO `sing_hobby` VALUES (2, 1002, '小红', '18', '2');
INSERT INTO `sing_hobby` VALUES (3, 1003, '小黑', '18', '1');
INSERT INTO `sing_hobby` VALUES (4, 1004, '小绿', '18', '1');
INSERT INTO `sing_hobby` VALUES (5, 1005, '小紫', '18', '2');
INSERT INTO `sing_hobby` VALUES (6, 1006, '小蓝', '18', '1');
INSERT INTO `sing_hobby` VALUES (7, 1007, '小黄', '18', '1');
INSERT INTO `sing_hobby` VALUES (8, 1008, '小白', '18', '1');
INSERT INTO `sing_hobby` VALUES (9, 1009, '小橙', '18', '2');
INSERT INTO `sing_hobby` VALUES (10, 1010, '小青', '18', '2');

1.INNER JOIN（内连接）

INNER JOIN 一般被译作内连接。内连接查询能将左表（表 A）和右表（表 B）中能关联起来的数据连接后返回。

一张图看懂 SQL 的各种 join 用法

SELECT <select_list> 
FROM Table_A A
INNER JOIN Table_B B
ON A.Key = B.Key

例子：

-- 内连接
SELECT
    sing.`name` as sing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sex
FROM
    sing_hobby sing
    inner JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num

2.LEFT JOIN（左连接）

LEFT JOIN 一般被译作左连接，也写作 LEFT OUTER JOIN。左连接查询会返回左表（表 A）中所有记录，不管右表（表 B）中有没有关联的数据。在右表中找到的关联数据列也会被一起返回。

一张图看懂 SQL 的各种 join 用法

SELECT <select_list>
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key

例子：

-- 左连接
SELECT
    sing.`name` as sing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sex
FROM
    sing_hobby sing
    LEFT JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num

3.RIGHT JOIN（右连接）

RIGHT JOIN 一般被译作右连接，也写作 RIGHT OUTER JOIN。右连接查询会返回右表（表 B）中所有记录，不管左表（表 A）中有没有关联的数据。在左表中找到的关联数据列也会被一起返回。

一张图看懂 SQL 的各种 join 用法

SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key

例子：

-- 右连接
SELECT
    sing.`name` as sing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sex
FROM
    sing_hobby sing
    RIGHT JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num

4.FULL OUTER JOIN（外连接）

FULL OUTER JOIN 一般被译作外连接、全连接，实际查询语句中可以写作 FULL OUTER JOIN 或 FULL JOIN。外连接查询能返回左右表里的所有记录，其中左右表里能关联起来的记录被连接后返回。

一张图看懂 SQL 的各种 join 用法

SELECT <select_list>
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.Key

注：mysql不支持外连接，可以使用 UNION ALL 代替，但要注意，如果要查询的两个表不是全部字段，那查询两个表的字段个数要相同，如下例子。

例子：

-- 外连接
SELECT sing.`name` as sing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sex 
FROM sing_hobby sing
LEFT JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num
UNION ALL
SELECT sing.`name` as sing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sex 
FROM sing_hobby sing
RIGHT JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num
WHERE sing.stu_num IS NULL

-- 外连接
SELECT
    sing.`name` as sing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sex
FROM
    sing_hobby sing
    FULL JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num

5.LEFT JOIN EXCLUDING INNER JOIN（左连接-内连接）

返回左表有，右表没有的关联数据记录集。

一张图看懂 SQL 的各种 join 用法

SELECT <select_list> 
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key
WHERE B.Key IS NULL

例子：

-- 左内连接
SELECT
    sing.`name` AS sing_name,
    sing.sex sing_sex,
    dancing.`name` dancing_name,
    dancing.sex dancing_sex 
FROM
    sing_hobby sing
    LEFT JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num 
WHERE
    dancing.stu_num IS NULL

6.RIGHT JOIN EXCLUDING INNER JOIN（右连接-内连接）

返回右表有，左表没有的关联数据记录集。

一张图看懂 SQL 的各种 join 用法

SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULL

例子：

-- 右内连接
SELECT
    sing.`name` AS sing_name,
    sing.sex sing_sex,
    dancing.`name` dancing_name,
    dancing.sex dancing_sex 
FROM
    sing_hobby sing
    RIGHT JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num 
WHERE
    sing.stu_num IS NULL

7.OUTER JOIN EXCLUDING INNER JOIN（外连接-内连接）

返回右表、左表没有的关联数据记录集。

一张图看懂 SQL 的各种 join 用法

SELECT <select_list>
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULL OR B.Key IS NULL

 例子：

-- 排除内连接的外连接
SELECT sing.`name` as sing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sex 
FROM sing_hobby sing
LEFT JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num
WHERE sing.stu_num IS NULL OR dancing.stu_num IS NULL
UNION ALL
SELECT sing.`name` as sing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sex 
FROM sing_hobby sing
RIGHT JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num
WHERE sing.stu_num IS NULL OR dancing.stu_num IS NULL

-- 排除内连接的外连接
SELECT
    sing.`name` AS sing_name,
    sing.sex sing_sex,
    dancing.`name` dancing_name,
    dancing.sex dancing_sex 
FROM
    sing_hobby sing
    FULL JOIN dancing_hobby dancing ON sing.stu_num = dancing.stu_num 
WHERE
    sing.stu_num IS NULL OR dancing.stu_num IS NULL

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原文地址：https://www.cnblogs.com/nananana/p/9354135.html