How to Accurately Count Distinct Site Logins in MySQL within 24 Hours?

Determining Distinct Login Counts in MySQL

In the realm of database management, it's often necessary to discern the unique occurrences of data within a given timeframe. To address this need in MySQL, the COUNT DISTINCT function proves invaluable, allowing us to determine the number of distinct values within a specified dataset.

A recent scenario presented the challenge of counting distinct visits to a particular site within the last 24 hours. The query initially employed, while appearing sound, yielded erroneous results with duplicate site IDs. This discrepancy posed the question: how to isolate and count only the distinct site logins?

The solution, as it turned out, lay in applying the COUNT DISTINCT function in conjunction with a GROUP BY clause. By isolating the site_id field, we ensured that only unique values were considered in the calculation. The revised query reads as follows:

SELECT
    COUNT(DISTINCT user_id) AS countUsers,
    COUNT(site_id) AS countVisits,
    site_id AS site
FROM
    cp_visits
WHERE
    ts >= DATE_SUB(NOW(), INTERVAL 1 DAY)
GROUP BY
    site_id

With this modified approach, the query now accurately reports the distinct site logins and their respective visit counts, providing the desired insights into user activity on the site in question.

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