Head First SQL

Chapter 5. Alter: Rewriting the Past

Ever wished you could correct the mistakes of your past? Well, now is your chance. By using the ALTER command, you can apply all the lessons you’ve been learning to tables you designed days, months, even years ago. Even better, you can do it without affecting your data. By the time you’re through here, you’ll know what normal really means, and you’ll be able to apply it to all your tables, past and present.

We need to make some changes

Greg wants to make a few more changes to his table, but he doesn’t want to lose any data.

Yes, you can use ALTER TABLE to add it easily.

In fact, we think you should take a stab at it yourself since you’ve already met the ALTER command. Do the next exercise to get your code!

Sharpen your pencil

Take a close look at the ALTER TABLE command we used to add the primary key column in Chapter 4, and see if you can come up with your own command to add a phone column that can hold 10 digits. Note that you won’t need to use all of the keywords in your new command.

ALTER TABLE my_contacts
ADD COLUMN contact_id INT NOT NULL AUTO_INCREMENT FIRST,
ADD PRIMARY KEY (contact_id);

Write your ALTER TABLE command here:

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