Explaining the SQL ALTER TABLE Statement

As suggested by the quiz question, let's demystify the SQL statement that adds a new column to an existing table.

The correct answer to the question is "ALTER TABLE Employees ADD COLUMN Salary int". This command in SQL is used to add a new column to a table. The keywords here are ALTER TABLE, ADD COLUMN and the column name along with its data type (Salary int).

ALTER TABLE is a DDL (Data Definition Language) command that allows you to alter the structure of the database. The ADD COLUMN clause is part of the ALTER TABLE command that's specifically used to add a new column.

In our example command, Employees is the name of the table we wish to alter. Salary is the new column we're introducing to the table and int is the data type of the new column, implying that the 'Salary' column will hold integer values.

Here's the general syntax of the command:

ALTER TABLE table_name
ADD COLUMN column_name datatype;

Using this structure, you can add any column to any table by replacing table_name with the table's name, column_name with the new column's name, and datatype with the type of data that will be stored in the new column.

For example, if you have an 'Employees' table and you want to add an 'Email' column which will hold string data, the statement would look like this:

ALTER TABLE Employees
ADD COLUMN Email varchar(255);

A point to notice is that the ALTER TABLE statement is immediate and cannot be rolled back in some databases. So always use this statement wisely and ensure you really want to make the change.

In addition, best practice suggests that the column name should be descriptive and concise. In this case, "Salary" correctly suggests that the column represents the salary of employees. Moreover, make sure the datatype is the correct choice for the data you anticipate the column holding. Misjudging the datatype can lead to errors and future difficulties.

In conclusion, the ALTER TABLE command is a powerful and handy SQL statement that allows modifications to be made to a database's structure even after it has been created. Understanding and correctly implementing it is very important to effectively manipulate your database schema.