SQL ALTER 关键字
ALTER TABLE
The ALTER TABLE command adds, deletes, or modifies columns in a table.
The ALTER TABLE command also adds and deletes various constraints in a table.
The following SQL adds an "Email" column to the "Customers" table
示例
ALTER TABLE Customers
ADD Email varchar(255);
The following SQL deletes the "Email" column from the "Customers" table
示例
ALTER TABLE Customers
DROP COLUMN Email;
ALTER COLUMN
The ALTER COLUMN command is used to change the data type of a column in a table.
The following SQL changes the data type of the column named "BirthDate" in the "Employees" table to type year
示例
ALTER TABLE Employees
ALTER COLUMN BirthDate year;
