Getting Started with SQL and Relational Databases/

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Unique Indexes

Unique Indexes

Learn to create unique indexes.

We'll cover the following...

Show existing customers

First, let’s see the current customers table again.

MySQL
select * from customers;

Now, let’s execute the following command. This will try to create a new customer, John Boo, but with the identity value equal to the identity of an existing customer (that of John Woo).

MySQL
insert into customers(name, identity) values ('John Boo','JW0001');

We’re doing a business error on purpose here. We’ve inserted the new customer with the wrong identity. However, the query has been successfully executed, and the new customer has ...