Preventing duplicate rows

Preventing duplicate rows is one of the most important aspects of data quality for any database. PostgreSQL offers some useful features in this area, extending beyond most relational databases.

Getting ready

Identify the set of columns that you wish to make unique. Does this apply to all rows, or just a subset of rows?

Let's start with our example table:

postgres=# SELECT * FROM newcust;
 customerid
------------
          1
          2
          3
          4
(4 rows)

How to do it...

To prevent duplicate rows, we need to create a unique index...