Adding a new column
Let’s suppose that you have created a table and populated it with plenty of data, only to discover you need an additional column. Not to worry. Here’s how to add the new column pages, which will be used to store the number of pages in a publication:
ALTER TABLE classics ADD pages SMALLINT UNSIGNED;
This adds the new column with the name pages using the UNSIGNED SMALLINT data type, sufficient to hold a value of up to 65,535—hopefully that’s more than enough for any book ever published!
And, if you ask MySQL to describe the updated table using the DESCRIBE command, as follows, you will see the change has been made.