【第二章】数据库的基本操作

MySQL数据库基本操作

创建表 create table
查看表结构 desc table, show create table
表完整性约束
修改表 alter table
复制表 create table ...
删除表 drop table

1）创建数据库：

2）创建表（表的基本操作）

表school.student1
字段字段字段
id name sex age
1 tom male 23 记录
2 jack male 21 记录
3 alice female 19 记录

语法：
create table 表名(
字段名1 类型[(宽度) 约束条件],
字段名2 类型[(宽度) 约束条件],
字段名3 类型[(宽度) 约束条件]
)[存储引擎字符集];
==在同一张表中，字段名是不能相同
==宽度和约束条件可选
==字段名和类型是必须的

mysql> CREATE DATABASE school;    　　    //创建数据库school
mysql> use school;
mysql> create table student1(
-> id int,
-> name varchar(50), 
-> sex enum('m','f'),
-> age int
-> );
Query OK, 0 rows affected (0.03 sec)


mysql> show tables;    //查看表（当前所在库）
+------------------+
| Tables_in_school |
+------------------+
| student1 |
+------------------+
1 row in set (0.00 sec)

mysql> select * from student1; //查询表中所有字段的值
Empty set (0.00 sec)

mysql> select name,age from student1;                //查询表中指定字段的值
Empty set (0.00 sec)

3）向表中插入内容

语法：
insert into 表名(字段1,字段2...) values(字段值列表...);

顺序插入：

mysql> desc student1;
+-------+---------------+------+-----+---------+-------+
| Field | Type          | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+-------+
| id    | int(11)       | YES  |     | NULL    |       |
| name  | varchar(50)   | YES  |     | NULL    |       |
| sex   | enum('m','f') | YES  |     | NULL    |       |
| age   | int(11)       | YES  |     | NULL    |       |
+-------+---------------+------+-----+---------+-------+
4 rows in set (0.32 sec)

mysql> insert into student1 values
    -> (1,'yanglt','m',28),
    -> (2,'chengdanjie','f',27)
    -> (3,'ylt','m',28);
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0  Warnings: 0

mysql> select * from student1;
+------+------------+------+------+
| id   | name       | sex  | age  |
+------+------------+------+------+
|    1 | yanglt     | m    |   28 |
|    2 | chendanjie | f    |   27 |
|    3 | ylt        | m    |   28 |
+------+------------+------+------+
3 rows in set (0.01 sec)

向指定字段插入：

mysql> insert into student1(name,age) values
    -> ('yangyang',15),
    -> ('chenchen',20);
Query OK, 2 rows affected (0.42 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from student1;
+------+------------+------+------+
| id   | name       | sex  | age  |
+------+------------+------+------+
|    1 | yanglt     | m    |   28 |
|    2 | chendanjie | f    |   27 |
|    3 | ylt        | m    |   28 |
| NULL | yangyang   | NULL |   15 |
| NULL | chenchen   | NULL |   20 |
+------+------------+------+------+
5 rows in set (0.00 sec)

mysql>