ALTER

In SQL, the ALTER statement is used to modify the structure of an existing database object, such as a table.

It allows you to add, modify, or drop columns, constraints, or other elements of a table without having to drop and recreate the entire table.

The basic syntax for the ALTER statement varies depending on the specific modification you want to make. Here are some examples.

Adding a column

To add a new column in a database table, you can use the ALTER command like this

ALTER TABLE table_name
ADD column_name data_type;

This statement adds a new column with the specified name and data type to the existing table.

Example

Suppose we have an employees table with the column id, firstName, lastName as shown below:

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by using ALTER, we can add a new column salary like this:

ALTER TABLE Employees
ADD salary INT;

After the query execution the Employee table will look like this:

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