About operations related to SQL ALTER TABLE statements

SQL ALTER TABLE statements are important in PHP operations and will be explained in this article.

SQL ALTER TABLE Syntax

To add columns to a table, use the following syntax:

ALTER TABLE table_name
ADD column_name datatype

To delete a column from a table, use the following syntax:

ALTER TABLE table_name
DROP COLUMN column_name

Note: Some database systems do not allow this method of deleting columns in a database table (DROP column column_name).

To change the data type of a column in a table, use the following syntax:

ALTER TABLE table_name
ALTER COLUMN column_name datatype

SQL ALTER TABLE Instance

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

We use the following SQL statements:

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.

Changing data type instances

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

We use the following SQL statements:

ALTER TABLE Persons
ALTER COLUMN Birthday Year

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

DROP COLUMN Instance

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

ALTER TABLE Person
DROP COLUMN Birthday

This article on the SQL ALTER table is related to the explanation, more learning materials clear focus on the PHP Chinese network can be viewed.