# Create Table 创建表

## 创建表

### CREATE TABLE table\_name (parm1, parm2, ...,parmN);

```sql
CREATE TABLE t_student (
	id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
	name VARCHAR(20) NOT NULL,
	gender ENUM("男","女") DEFAULT "男",
	birthday DATE NOT NULL,
	tel CHAR(11)
) ;



```

我们我们创建了一个 名叫 student 的表格，里面有5个字段(也就是5列)，分别是

1. id， 无符号整型，主键约束。所谓主键就是用来唯一标志这一行的数据的一个变量，在一张表中，主键不允许有重复。AUTO\_INCREMENT,  默认起始值为1，以后依次增加1；
2. name, 字符串类型，最大长度为20，不允许为NULL
3. gender, 枚举，默认 "男”
4. birthday, 日期类型，不允许为NULL
5. tel, 字符串类型，固定长度为11，允许为NULL

我们接着往下创建两个表

```sql
CREATE TABLE t_dept(
	deptno INT UNSIGNED PRIMARY KEY,
	deptname VARCHAR(20) NOT NULL UNIQUE
);

CREATE TABLE t_emp(
	deptno INT UNSIGNED PRIMARY KEY,
	name VARCHAR(20) NOT NULL,
	FOREIGN KEY (deptno) REFERENCES t_dept (deptno)
);
	
```

特别的是 t\_dept 中的 deptname 使用了 **UNIQUE 约束, 表示值必须唯一，但是可以为NULL**

**外键宇约束 FOREIGN KEY （deptno）REFERENCES  t\_dept (deptno), 表示 当期表内的 deptno 与 外部表的 t\_dept内的 deptno产生关联。其中外部的字段必须为PRIMARY KEY。**

### 向表中插入数据

### INSERT INTO table\_name VALUES (value1,value2, ...,valueN);

```sql
INSERT INTO t_student VALUES(1,"张三","男","1995-06-01","12345678900" );



```

### INSERT INTO table\_name （field1,field2, ..., fieldN） VALUES (value1,value2, ...,valueN);

```sql
INSERT INTO t_student (name,gender,birthday,tel) VALUES("李四","男","1998-02-11","01234567890" );
```

## 查看表格结构

```sql
DESC student;
```

## 查看当前数据库内所有表

```sql
SHOW TABLES;
```

## 删除表

```sql
DROP TABLE student;
```


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