How to not count rows twice if they have same value in mySQL?

Question

I have a visitor tracking system. I track visitor ips and browser. I can count total visits (total rows), but how can I count unique visits ?

Answer 1

您可以使用Distinct ：

SELECT Count(DISTINCT visits) from Table;

Answer 2

Use GROUP BY on IP, or IP+browser! SELECT COUNT(ip) FROM yourtable GROUP BY ip

Answer 3

Something like this will give you "unique visitors" as measured by distinct browser/IP hits:

SELECT COUNT(*) AS unique_visitors FROM (
    SELECT DISTINCT ip, browser FROM visitors
) a