- 数据类型
- 数据表操作
数据类型
![](https://img.haomeiwen.com/i10186693/2e761ef6a0cb92ed.png)
![](https://img.haomeiwen.com/i10186693/33444f8b51e24924.png)
选择最合理最适合的数据类型,而不是选择最大的数据类型。
年龄用整型,工资用浮点型
![](https://img.haomeiwen.com/i10186693/0a217b27a715d704.png)
![](https://img.haomeiwen.com/i10186693/e4eeb2e30e1876ff.png)
![](https://img.haomeiwen.com/i10186693/5fa3efbe0d6173ee.png)
char定长类型,如果为5个字符,只有abc,则后两位为空格
varchar变长类型
1个字节是8bit
ENUM枚举值,如性别选择
SET集合,最多有64个成员
数据表
行:记录,列:字段
![](https://img.haomeiwen.com/i10186693/731d59bb93f272a4.png)
USE
- 打开数据库
- USE 数据库名称
![](https://img.haomeiwen.com/i10186693/6217568a4ca79916.png)
![](https://img.haomeiwen.com/i10186693/91472dcae38497b3.png)
![](https://img.haomeiwen.com/i10186693/55a9e980fe9dd12c.png)
CREATE TABLE一定不可以省略,IF NOT EXISTS 可以省略
table_name数据表名
column_name列名称(根据项目分析得到,不是凭空想象)
data_type数据类型
![](https://img.haomeiwen.com/i10186693/be437d2e2ce4e103.png)
查看数据表列表
![](https://img.haomeiwen.com/i10186693/895d462c983e253a.png)
![](https://img.haomeiwen.com/i10186693/a7558cdb7e7caaf7.png)
查看数据表结构
![](https://img.haomeiwen.com/i10186693/2f9770b2949553bb.png)
插入记录
![](https://img.haomeiwen.com/i10186693/075bce751fa58b62.png)
记录查找
*在这里表示是字段的过滤
![](https://img.haomeiwen.com/i10186693/df8e1ba73bc0574c.png)
空值与非空
不能用在同一个字段上,不可能既为空,又为非空。
![](https://img.haomeiwen.com/i10186693/049ce8f53ff99a9b.png)
![](https://img.haomeiwen.com/i10186693/3ead3f44b3c2d05d.png)
AUTO_INCREMENT
![](https://img.haomeiwen.com/i10186693/ef58f29465a43723.png)
报错原因:自动编号的字段必须定义成主键。
PRIMARY KEY
![](https://img.haomeiwen.com/i10186693/91ac03d21a31f9c7.png)
![](https://img.haomeiwen.com/i10186693/3b07cf297f6ec968.png)
AUTO_INCREMENT必须和主键一起使用,烦主键不一定要和AUTO_INCREMENT一起使用。不可以使用相同的键。
![](https://img.haomeiwen.com/i10186693/3306ff312128a3b5.png)
UNIQUE KEY
![](https://img.haomeiwen.com/i10186693/5764270df59da6a6.png)
![](https://img.haomeiwen.com/i10186693/31a6f2bed8eea3af.png)
主键约束一张表只有一个
唯一约束一张表可以有多个
DEFAULT
![](https://img.haomeiwen.com/i10186693/f9b590a1a14b7dc7.png)
![](https://img.haomeiwen.com/i10186693/f54b825b4886612a.png)
![](https://img.haomeiwen.com/i10186693/729d74299413f852.png)
![](https://img.haomeiwen.com/i10186693/7e9f576d3f3a3769.png)
![](https://img.haomeiwen.com/i10186693/29eedd255022c29a.png)
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