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。

SELECT

FROMTable_A AINNER JOINTable_B BON A.Key = B.Key

例子：

--内连接

SELECTsing.`name`assing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sexFROMsing_hobby singinner 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。

SELECT

FROMTable_A ALEFT JOINTable_B BON A.Key = B.Key

例子：

--左连接

SELECTsing.`name`assing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sexFROMsing_hobby singLEFT 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。

SELECT

FROMTable_A ARIGHT JOINTable_B BON A.Key = B.Key

例子：

--右连接

SELECTsing.`name`assing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sexFROMsing_hobby singRIGHT 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。

SELECT

FROMTable_A AFULL OUTER JOINTable_B BON 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` assing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sexFROMsing_hobby singLEFT JOIN dancing_hobby dancing ON sing.stu_num =dancing.stu_numUNION ALL

SELECT sing.`name` assing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sexFROMsing_hobby singRIGHT JOIN dancing_hobby dancing ON sing.stu_num =dancing.stu_numWHERE sing.stu_num IS NULL

--外连接

SELECTsing.`name`assing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sexFROMsing_hobby singFULL 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。

SELECT

FROMTable_A ALEFT JOINTable_B BON A.Key = B.Key

WHERE B.Key IS NULL

例子：

--左内连接

SELECTsing.`name`ASsing_name,

sing.sex sing_sex,

dancing.`name` dancing_name,

dancing.sex dancing_sexFROMsing_hobby singLEFT JOIN dancing_hobby dancing ON sing.stu_num =dancing.stu_numWHEREdancing.stu_numIS 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。

SELECT

FROMTable_A ARIGHT JOINTable_B BON A.Key = B.Key

WHERE A.Key IS NULL

例子：

--右内连接

SELECTsing.`name`ASsing_name,

sing.sex sing_sex,

dancing.`name` dancing_name,

dancing.sex dancing_sexFROMsing_hobby singRIGHT JOIN dancing_hobby dancing ON sing.stu_num =dancing.stu_numWHEREsing.stu_numIS 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。

SELECT

FROMTable_A AFULL OUTER JOINTable_B BON 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` assing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sexFROMsing_hobby singLEFT JOIN dancing_hobby dancing ON sing.stu_num =dancing.stu_numWHERE sing.stu_num IS NULL OR dancing.stu_num IS NULL

UNION ALL

SELECT sing.`name` assing_name,sing.sex sing_sex,dancing.`name` dancing_name,dancing.sex dancing_sexFROMsing_hobby singRIGHT JOIN dancing_hobby dancing ON sing.stu_num =dancing.stu_numWHERE sing.stu_num IS NULL OR dancing.stu_num IS NULL

--排除内连接的外连接

SELECTsing.`name`ASsing_name,

sing.sex sing_sex,

dancing.`name` dancing_name,

dancing.sex dancing_sexFROMsing_hobby singFULL JOIN dancing_hobby dancing ON sing.stu_num =dancing.stu_numWHEREsing.stu_numIS NULL OR dancing.stu_num IS NULL