Related operations of SQL ALTER TABLE statement

SQL ALTER TABLE statement is very important in PHP operation, this article will explain it.

SQL ALTER TABLE syntax

To add columns to the 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

Comments: Some database systems do not allow this method of deleting columns in database tables (DROP COLUMN column_name).

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

ALTER TABLE table_name
ALTER COLUMN column_name datatype

SQL ALTER TABLE Example

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

We use the following SQL statement:

ALTER TABLE Persons
ADD Birthday date

Please note that the new column "Birthday" The type is date, which can store dates. The data type specifies the type of data that can be stored in the column.

Change Data Type Example

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

We use the following SQL statement:

ALTER TABLE Persons
ALTER COLUMN Birthday year

Please note that the data type of the "Birthday" column is year, Can store year in 2-digit or 4-digit format.

DROP COLUMN Example

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

ALTER TABLE Person
DROP COLUMN Birthday

This article provides relevant explanations on SQL ALTER TABLE. For more learning materials, please pay attention to the php Chinese website to view.

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