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SQL Alter


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ALTER TABLE
改变表

The ALTER TABLE statement is used to add or drop columns in an existing table.
ALTER TABLE语句可以用来给现有的表进行添加或是删除栏目的操作。

ALTER TABLE table_name 
ADD column_name datatype
ALTER TABLE table_name 
DROP COLUMN column_name

Note: Some database systems don't allow the dropping of a column in a database table (DROP COLUMN column_name).
注意:一些数据库系统不允许删除表中的栏目(DROP COLUMN 栏目名)


Person表:

LastName FirstName Address
Pettersen Kari Storgt 20


Example
举例

To add a column named "City" in the "Person" table:
给这张"Person"表加一个名为"City"的栏目:

ALTER TABLE Person ADD City varchar(30)

Result:
结果:

LastName FirstName Address City
Pettersen Kari Storgt 20  

Example
举例

To drop the "Address" column in the "Person" table:
删除"Person"表中的"Address"栏目

ALTER TABLE Person DROP COLUMN Address

Result:
结果:

LastName FirstName City
Pettersen Kari  

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