MySQL插入外键
创建外键mysql> CREATE TABLE `study_record` (
-> `id` int(11) NOT NULL,
-> `day` int NOT NULL,
-> `status` char(32) NOT NULL,
-> `stu_id` int(11) NOT NULL,
-> PRIMARY KEY (`id`),
-> KEY `fk_student_key` (`stu_id`),
-> CONSTRAINT `fk_student_key` FOREIGN KEY (`stu_id`) REFERENCES `student` (`id`)
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> alter table study_record modify id int auto_increment;
Query OK, 0 rows affected (0.07 sec)
Records: 0Duplicates: 0Warnings: 0
mysql> insert into study_record (day,status,stu_id) values(1,'Yes',4);
Query OK, 1 row affected (0.00 sec)
mysql> insert into study_record (day,status,stu_id) values(1,'Yes',1);
Query OK, 1 row affected (0.00 sec)
mysql>
mysql> select * from study_record;
+----+-----+--------+--------+
| id | day | status | stu_id |
+----+-----+--------+--------+
|1 | 1 | Yes | 4 |
|2 | 1 | Yes | 1 |
+----+-----+--------+--------+
2 rows in set (0.00 sec)
mysql> insert into study_record (day,status,stu_id) values(2,'No',1);
Query OK, 1 row affected (0.01 sec)
mysql> select * from study_record;
+----+-----+--------+--------+
| id | day | status | stu_id |
+----+-----+--------+--------+
|1 | 1 | Yes | 4 |
|2 | 1 | Yes | 1 |
|3 | 2 | No | 1 |
+----+-----+--------+--------+
3 rows in set (0.00 sec)
mysql> select * from study_record;
+----+-----+--------+--------+
| id | day | status | stu_id |
+----+-----+--------+--------+
|1 | 1 | Yes | 4 |
|2 | 1 | Yes | 1 |
|3 | 2 | No | 1 |
+----+-----+--------+--------+
3 rows in set (0.00 sec)
mysql> delete from study_record where id=3;
Query OK, 1 row affected (0.02 sec)
mysql> select * from study_record;
+----+-----+--------+--------+
| id | day | status | stu_id |
+----+-----+--------+--------+
|1 | 1 | Yes | 4 |
|2 | 1 | Yes | 1 |
+----+-----+--------+--------+
2 rows in set (0.00 sec)
mysql>
多表查询：
mysql> create table A(
-> a int not null);
Query OK, 0 rows affected (0.04 sec)
mysql> create table B( b int not null);
Query OK, 0 rows affected (0.02 sec)
mysql> insert into A (a) values(1);
Query OK, 1 row affected (0.01 sec)
mysql> insert into A (a) values(2);
Query OK, 1 row affected (0.00 sec)
mysql> insert into A (a) values(3);
Query OK, 1 row affected (0.00 sec)
mysql> insert into A (a) values(4);
Query OK, 1 row affected (0.00 sec)
mysql> insert into B (b) values(3);
Query OK, 1 row affected (0.02 sec)
mysql> insert into B (b) values(4);
Query OK, 1 row affected (0.00 sec)
mysql> insert into B (b) values(5);
Query OK, 1 row affected (0.00 sec)
mysql> insert into B (b) values(6);
Query OK, 1 row affected (0.00 sec)
mysql> insert into B (b) values(7);
Query OK, 1 row affected (0.00 sec)
mysql> select * from A;
+---+
| a |
+---+
| 1 |
| 2 |
| 3 |
| 4 |
+---+
4 rows in set (0.00 sec)
mysql> select * from B;
+---+
| b |
+---+
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
+---+
5 rows in set (0.00 sec)
Inner join语法 其实就是只显示2个表的交集
mysql> select * from A inner join B on A.a = B.b;
+---+---+
| a | b |
+---+---+
| 3 | 3 |
| 4 | 4 |
+---+---+
2 rows in set (0.00 sec)
第二种语法
mysql> select A.*,B.* from A,B where A.a=B.b;
+---+---+
| a | b |
+---+---+
| 3 | 3 |
| 4 | 4 |
+---+---+
2 rows in set (0.00 sec)
left join 语法求差级
mysql> select * from A left join B on A.a = B.b;
+---+------+
| a | b |
+---+------+
| 3 | 3 |
| 4 | 4 |
| 1 | NULL |
| 2 | NULL |
+---+------+
4 rows in set (0.00 sec)
mysql> select * from B left join A on A.a = B.b;
+---+------+
| b | a |
+---+------+
| 3 | 3 |
| 4 | 4 |
| 5 | NULL |
| 6 | NULL |
| 7 | NULL |
+---+------+
5 rows in set (0.00 sec)
right join
mysql> select * from A right join B on A.a = B.b;
+------+---+
| a | b |
+------+---+
| 3 | 3 |
| 4 | 4 |
| NULL | 5 |
| NULL | 6 |
| NULL | 7 |
+------+---+
5 rows in set (0.01 sec)
fulljoin 求并集
mysql 并不直接支持full join,but 总是难不到我们
mysql> select * from A left join B on A.a=B.b union select * from A right join B on A.a=B.b;
+------+------+
| a | b |
+------+------+
| 3 | 3 |
| 4 | 4 |
| 1 | NULL |
| 2 | NULL |
| NULL | 5 |
| NULL | 6 |
| NULL | 7 |
+------+------+
7 rows in set (0.01 sec)
mysql>
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