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Book Overview & Buying
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Table Of Contents
The MySQL Workshop
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In addition to creating tables, it is also possible to modify existing tables. This can be done using an ALTER query. An ALTER query uses the following syntax:
ALTER TABLE [table_name] [alter_options]
ALTER queries can be used for a number of purposes. One common reason is to change how a field in a table is defined. For example, suppose we have a customer table that contains a field for username. Currently, it allows for a VARCHAR value of size 15, but we want to extend this to be size 30. To do this, we can use an ALTER query, as follows:
ALTER TABLE customer MODIFY username VARCHAR(30);
We can also use the ALTER query to add an index to our table. To do this, we first need to create the index using a CREATE query. So, for example, suppose we now wanted to add an index to the username of our customer table. First, we create the index for username:
CREATE UNIQUE INDEX 'idx_username' ON customer('username')
The next exercise...