alter table add colne
时间: 2023-09-23 22:06:45 浏览: 86
There is a typo in your statement.
The correct syntax to add a column to an existing table is:
```
ALTER TABLE table_name ADD column_name data_type;
```
For example, to add a column called "email" of type VARCHAR(255) to a table called "users", the statement would be:
```
ALTER TABLE users ADD email VARCHAR(255);
```
相关问题
alter table 所有语法
alter table 语句是用于修改现有数据库表的结构,可以通过以下语法来实现:
1. 添加列
ALTER TABLE table_name ADD column_name datatype;
2. 修改列
ALTER TABLE table_name MODIFY column_name datatype;
3. 重命名列
ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name;
4. 删除列
ALTER TABLE table_name DROP COLUMN column_name;
5. 修改表名
ALTER TABLE table_name RENAME TO new_table_name;
6. 添加主键
ALTER TABLE table_name ADD PRIMARY KEY (column_name);
7. 删除主键
ALTER TABLE table_name DROP PRIMARY KEY;
8. 添加外键
ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY (column_name) REFERENCES other_table (column_name);
9. 删除外键
ALTER TABLE table_name DROP CONSTRAINT constraint_name;
10. 添加索引
ALTER TABLE table_name ADD INDEX index_name (column_name);
11. 删除索引
ALTER TABLE table_name DROP INDEX index_name;
alter table语句怎么用
alter table语句用于修改数据库表的结构,例如添加、删除、修改列或约束等。下面是alter table语句的一些常见用法:
1. 添加列
ALTER TABLE 表名 ADD 列名 数据类型;
例如:ALTER TABLE student ADD age INT;
2. 删除列
ALTER TABLE 表名 DROP COLUMN 列名;
例如:ALTER TABLE student DROP COLUMN age;
3. 修改列
ALTER TABLE 表名 MODIFY COLUMN 列名 新数据类型;
例如:ALTER TABLE student MODIFY COLUMN age FLOAT;
4. 添加主键
ALTER TABLE 表名 ADD PRIMARY KEY (列名);
例如:ALTER TABLE student ADD PRIMARY KEY (id);
5. 删除主键
ALTER TABLE 表名 DROP PRIMARY KEY;
例如:ALTER TABLE student DROP PRIMARY KEY;
6. 添加外键
ALTER TABLE 表名 ADD FOREIGN KEY (列名) REFERENCES 关联表名(关联列名);
例如:ALTER TABLE score ADD FOREIGN KEY (student_id) REFERENCES student(id);
7. 删除外键
ALTER TABLE 表名 DROP FOREIGN KEY 外键名称;
例如:ALTER TABLE score DROP FOREIGN KEY fk_score_student;
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