How to count unique values?

Question

I am trying get the number of unique ip_addresses (in this case '3'). The table looks like this:

Structure:

CREATE TABLE bandits (
  key text NOT NULL,
  ip_address inet,
  offence text,
  count bigint DEFAULT 1);

Data:

COPY bandits (key, ip_address, offence, count) FROM stdin;
127.0.0.1_testing   127.0.0.1  testing  1
127.0.0.2_testing   127.0.0.2  testing  3
127.0.0.2_testing2  127.0.0.2  testing2 1
127.0.0.3_testing   127.0.0.3  testing  1

Answer 1

SELECT COUNT(DISTINCT ip_address) FROM bandits