操作表
增:
语法:create table 表名(
)chart utf8;
列约束:(*********************)
auto_increment : 自增 1 用于ID值
primary key : 主键索引,加快查询速度, 列的值不能重复
not noll 标识该字段不能为空
default 为该字段设置默认值
例子1:
create table t1(
id int,
name char(5)
)charset=utf8;
Query OK, 0 rows affected (0.72 sec) #### 如果回显是queryok,代表创建成功
增加数据:
语法:
insert into 表名 (列1, 列2) values (值1,'值2');
例子:
insert into t1 (id, name) values (1, 'zekai');
insert into t1 (id, name) values (1, 'zekai2');
查询数据:
语法:
select 列1, 列2 from 表名; (*代表查询所有的列)
例子:
mysql> select * from t1;
+------+-------+
| id | name |
+------+-------+
| 1 | zekai |
+------+-------+
1 row in set (0.00 sec)
例子2:
create table t2(
id int auto_increment primary key,
name char(10)
)charset=utf8;
insert into t2 (name) values ('zekai1');
例子3:
create table t3(
id int unsigned auto_increment primary key,
name char(10) not null default 'xxx',
age int not null default 0
)charset=utf8;
mysql> insert into t3 (age) values (10);
Query OK, 1 row affected (0.05 sec)
mysql> select * from t3;
+----+------+-----+
| id | name | age |
+----+------+-----+
| 1 | xxx | 10 |
+----+------+-----+
列类型
create table 表名(
字段名 列类型 unsigned [可选的参数], ### 记住加逗号
字段名 列类型 [可选的参数], ### 记住加逗号
字段名 列类型 [可选的参数] ### 最后一行不加逗号
.....
)charset=utf8; #### 后面加分号
- 数字
- 整型
tinyint (-128,127) (0,255)
smallint (-32768,32767) (0,65535)
int (**********)(-2 147 483 648,2 147 483 647) (0,4 294 967 295)推荐使用
mediumint
bigint
a.整数类型
b.取值范围
c.unsigned 加上代表不能取负数 只适用于整型
应用场景:
根据公司业务的场景,来选取合适的类型
- 浮点型 (***********)
create table t5(
id int auto_increment primary key,
salary decimal(16,10),
num float
)charset=utf8;
float: 不一定精确 (m,d)m是数字总个数,d是小数点后个数
decimal: 非常的精确的数字 (5000.23) decimal(6, 2) m是数字总个数(负号不算),d是小数点后个数。
例子1:
正好 10 位:
mysql> insert into t5 (salary, num) values (500023.2312345678, 5000.2374837284783274832);
Query OK, 1 row affected (0.04 sec)
mysql> select * from t5;
+----+-------------------+---------+
| id | salary | num |
+----+-------------------+---------+
| 1 | 500023.2312345678 | 5000.24 |
+----+-------------------+---------+
1 row in set (0.00 sec)
例子2:
少于10位:用0 补足
mysql> insert into t5 (salary, num) values (500023.231234567, 5000.2374837284783274832);
Query OK, 1 row affected (0.04 sec)
mysql> select * from t5;
+----+-------------------+---------+
| id | salary | num |
+----+-------------------+---------+
| 1 | 500023.2312345678 | 5000.24 |
| 2 | 500023.2312345670 | 5000.24 |
+----+-------------------+---------+
例子3:
多于10位:四舍五入
mysql> insert into t5 (salary, num) values (500023.23123456789, 5000.2374837284783274832);
Query OK, 1 row affected, 1 warning (0.03 sec)
mysql> select * from t5;
+----+-------------------+---------+
| id | salary | num |
+----+-------------------+---------+
| 1 | 500023.2312345678 | 5000.24 |
| 2 | 500023.2312345670 | 5000.24 |
| 3 | 500023.2312345679 | 5000.24 |
+----+-------------------+---------+
- 字符串
- char(长度) : 定长
create table t6(
id unsigned int auto_increment primary key,
name char(10) not null default 'xxx',
)charset=utf8;
- varchar(长度):变长
create table t6(
id int auto_increment primary key,
name varchar(10) not null default 'xxx'
)charset=utf8;
mysql> insert into t6 (name) values ('hello');
Query OK, 1 row affected (0.03 sec)
mysql> select * from t6;
+----+-------+
| id | name |
+----+-------+
| 1 | hello |
+----+-------+
1 row in set (0.00 sec)
mysql> insert into t6 (name) values ('hellodbsabdsjabjdsa');
ERROR 1406 (22001): Data too long for column 'name' at row 1
区别:
char: 定长, 无论插入的字符是多少个,永远固定占规定的长度
场景:
1. 身份证
2. 手机号 char(11)
3. md5加密之后的值,比如密码 等 char(32)
varchar: 变长, 根据插入的字符串的长度来计算所占的字节数,但是有一个字节是用来保存字符串的大小的
注意:如果, 不能确定插入的数据的大小, 一般建议使用 varchar(255)
- 时间日期类型
YEAR
YYYY(1901/2155)
DATE
YYYY-MM-DD(1000-01-01/9999-12-31)
TIME
HH:MM:SS('-838:59:59'/'838:59:59')
DATETIME (***************************)
YYYY-MM-DD HH:MM:SS(1000-01-01 00:00:00/9999-12-31 23:59:59 Y)
TIMESTAMP
YYYYMMDD HHMMSS(1970-01-01 00:00:00/2037 年某时)
例子:
create table t8(
d date,
t time,
dt datetime
);
mysql> insert into t8 values(now(),now(),now());
Query OK, 1 row affected, 1 warning (0.08 sec)
mysql> select * from t8;
+------------+----------+---------------------+
| d | t | dt |
+------------+----------+---------------------+
| 2019-10-29 | 10:49:51 | 2019-10-29 10:49:51 |
+------------+----------+---------------------+
1 row in set (0.00 sec)
insert into t8 values(now(),now(),now());
- 枚举
列出所有的选项
create table t9 (
id int auto_increment primary key,
gender enum('male','female')
)charset utf8;
mysql> insert into t9 (gender) values ('male');
Query OK, 1 row affected (0.04 sec)
mysql> insert into t9 (gender) values ('female');
Query OK, 1 row affected (0.03 sec)
mysql> insert into t9 (gender) values ('dshajjdsja');