SQL Basic Operations--alter

The ALTER table statement is used to add, modify, or delete columns in an existing table.

Persons table:

Id	LastName	FirstName	Address	City
1	Adams	John	Oxford Street	London
2	Bush	George	Fifth Avenue	New York
3	Carter	Thomas	Changan Street	Beijing

Now, we want to add a new column named "Birthday" in the table "Persons".

ALTER TABLE Persons ADD Birthday Date

Note that the type of the new column "Birthday" is date and can hold the date. The data type specifies the type of data that can be stored in the column.

The new "Persons" table looks like this:

Id	LastName	FirstName	Address	City	Birthday
1	Adams	John	Oxford Street	London
2	Bush	George	Fifth Avenue	New York
3	Carter	Thomas	Changan Street	Beijing

Now we want to change the data type of the "Birthday" column in the "Persons" table.

ALTER TABLE Persons ALTER COLUMN  Year

Note that the data type of the "Birthday" column is year, which can hold 2-bit or 4-bit formats.

Next, we delete the "Birthday" column in the "Person" table:

ALTER TABLE  Person DROP COLUMN Birthday

Id	LastName	FirstName	Address	City
1	Adams	John	Oxford Street	London
2	Bush	George	Fifth Avenue	New York
3	Carter	Thomas	Changan Street	Beijing

Reference: SQL ALTER TABLE Statement

SQL Basic Operations--alter