mysql建表

mysql学生表

CREATE TABLE `courses` (
`id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增id',
`student` VARCHAR(255) DEFAULT NULL COMMENT '学生',
`class` VARCHAR(255) DEFAULT NULL COMMENT '课程',
`score` INT(255) DEFAULT NULL COMMENT '分数',
PRIMARY KEY (`id`),
UNIQUE KEY `course` (`student`, `class`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

插入数据

INSERT INTO `courses`(`student`, `class`, `score`) VALUES('A', 'Math', 90);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('A', 'Chinese', 80);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('A', 'English', 70);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('A', 'History', 80);INSERT INTO `courses`(`student`, `class`, `score`) VALUES('B', 'Math', 73);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('B', 'Chinese', 60);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('B', 'English', 70);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('B', 'History', 90);INSERT INTO `courses`(`student`, `class`, `score`) VALUES('C', 'Math', 70);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('C', 'Chinese', 50);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('C', 'English', 20);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('C', 'History', 10);INSERT INTO `courses`(`student`, `class`, `score`) VALUES('D', 'Math', 53);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('D', 'Chinese', 32);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('D', 'English', 99);
INSERT INTO `courses`(`student`, `class`, `score`) VALUES('D', 'History', 100);

建表，学生和id

CREATE TABLE `phone` (
`id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增id',
`student` VARCHAR(255) DEFAULT NULL COMMENT '学生',
`phone` VARCHAR(255) DEFAULT NULL COMMENT '电话',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

group by

mysql> select * from courses;
+----+---------+---------+-------+
| id | student | class   | score |
+----+---------+---------+-------+
|  1 | A       | Math    |    90 |
|  2 | A       | Chinese |    80 |
|  3 | A       | English |    70 |
|  4 | A       | History |    80 |
|  5 | B       | Math    |    73 |
|  6 | B       | Chinese |    60 |
|  7 | B       | English |    70 |
|  8 | B       | History |    90 |
|  9 | C       | Math    |    70 |
| 10 | C       | Chinese |    50 |
| 11 | C       | English |    20 |
| 12 | C       | History |    10 |
| 13 | D       | Math    |    53 |
| 14 | D       | Chinese |    32 |
| 15 | D       | English |    99 |
| 16 | D       | History |   100 |
+----+---------+---------+-------+
16 rows in set (0.00 sec)mysql> select class, min(score) from courses group by class;
+---------+------------+
| class   | min(score) |
+---------+------------+
| Math    |         53 |
| Chinese |         32 |
| English |         20 |
| History |         10 |
+---------+------------+
4 rows in set (0.00 sec)mysql> select class from courses group by class;
+---------+
| class   |
+---------+
| Chinese |
| English |
| History |
| Math    |
+---------+
4 rows in set (0.00 sec)

inner join

mysql> select *  from phone;
+----+---------+-------------+
| id | student | phone       |
+----+---------+-------------+
|  1 | A       | 123123123   |
|  2 | B       | 12312312322 |
|  3 | C       | 321321      |
+----+---------+-------------+
3 rows in set (0.00 sec)mysql> select *  from courses;
+----+---------+---------+-------+
| id | student | class   | score |
+----+---------+---------+-------+
|  1 | A       | Math    |    90 |
|  2 | A       | Chinese |    80 |
|  3 | A       | English |    70 |
|  4 | A       | History |    80 |
|  5 | B       | Math    |    73 |
|  6 | B       | Chinese |    60 |
|  7 | B       | English |    70 |
|  8 | B       | History |    90 |
|  9 | C       | Math    |    70 |
| 10 | C       | Chinese |    50 |
| 11 | C       | English |    20 |
+----+---------+---------+-------+
11 rows in set (0.00 sec)mysql> select a.phone, b.class from phone a inner join courses b on a.student= b.student;
+-------------+---------+
| phone       | class   |
+-------------+---------+
| 123123123   | Chinese |
| 123123123   | English |
| 123123123   | History |
| 123123123   | Math    |
| 12312312322 | Chinese |
| 12312312322 | English |
| 12312312322 | History |
| 12312312322 | Math    |
| 321321      | Chinese |
| 321321      | English |
| 321321      | Math    |
+-------------+---------+
11 rows in set (0.00 sec)mysql> select distinct a.phone, b.student from phone a inner join courses b on a.student= b.student;
+-------------+---------+
| phone       | student |
+-------------+---------+
| 123123123   | A       |
| 12312312322 | B       |
| 321321      | C       |
+-------------+---------+
3 rows in set (0.00 sec)