Making sure each record has a unique value

Solution

Either use the UNIQUE modifier on the field when defining the table ref, or create a UNIQUE index on that field (or fields) after the table is created ref.

Discussion

It is customary to make sure there is a unique code for each record in a table (a primary key) so you can select that record and no other. If you don't know why this is a good idea, search the web for terms like "Normalisation" and "Normal forms".

When creating a table all the following fields will be forced to be unique.

CREATE TABLE foo (
  field1 serial
  field2 text UNIQUE
  field3 text PRIMARY KEY
  field4 text,
  field5 text
PRIMARY KEY (field4)
);
CREATE UNIQUE INDEX foo_field5_idx ON foo(field5);
   

The serial type creates a UNIQUE NOT NULL int4 and attaches it to a sequence.

The UNIQUE modifier creates a unique index on the value. You might want to add NOT NULL as well if the field should always have a value.

The PRIMARY KEY is equivalent to UNIQUE NOT NULL.

Which form you want to use will depend upon context and your personal preferences.