2.1 MySQL约束条件

约束条件

NULL            允许为空，默认设置
NOT NULL        不允许为空
Key             索引类型
Default         设置默认值，缺省为NULL
PRIMARY KEY 主键，所有记录中此字段的值不能重复，且不能为NULL
UNIQUE KEY 唯一键，所有记录中此字段的值不能重复，但可以为NULL
CHARACTER SET name 指定一个字符集

mysql> create table t1( name char(10) not null, gender enum("man","woman","no") default "no", age tinyintunsigned );
mysql> desc t1;
+--------+--------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------------------+------+-----+---------+-------+
| name | char(10) | NO | | NULL | |
| gender | enum('man','woman','no') | YES | | no | |
| age | tinyint(3) unsigned | YES | | NULL | |
+--------+--------------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

当不给默认字段赋值时，选择默认值
mysql> insert into t1(name) values("lw");
Query OK, 1 row affected (0.00 sec)

mysql> select * from t1;
+------+--------+------+
| name | gender | age  |
+------+--------+------+
| lw   | no     | NULL |
+------+--------+------+
1 row in set (0.00 sec)

 

直接指定字符集
mysql> create table db1.t1(name varchar(10)) character set utf8;
Query OK, 0 rows affected (0.02 sec)

mysql> desc db1.t1;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| name  | varchar(10) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
1 row in set (0.00 sec)