Cohort analysis in SQL

Question

Looking to do some cohort analysis on a userbase. We have 2 tables \"users\" and \"sessions\", where users and sessions both have a \"created_at\" field. I\'m looking to f

Answer 1

This answer inverts the output table that @Newy wanted so the cohorts are the rows instead of the columns, and uses absolute dates instead of relative ones.

I was looking for a query that would give me something like this:

Date        d0  d1  d2  d3  d4  d5  d6
2016-11-03  3   1   0   0   0   0   0
2016-11-04  4   2   0   1   0   0   *
2016-11-05  7   0   1   1   0   *   *
2016-11-06  7   3   1   1   *   *   *
2016-11-07  13  5   1   *   *   *   *
2016-11-08  4   0   *   *   *   *   *
2016-11-09  1   *   *   *   *   *   *

I was looking for the number of users that signed up a certain date, then how many of those users returned 1 day later, 2 days later, etc. So on 2016-11-07 13 users signed up and had a session, then 5 of those users came back 1 day later, then one user came back 2 days later, etc.

I took the first subquery of @Andriy M's large query and modified it to give me the date a user signed up, not the days relative to the current date:

SELECT
    id,
    DATE(created_at) AS DayOffset
  FROM users
  WHERE created_at >= CURDATE() - INTERVAL 6 DAY

Then the LEFT JOIN subquery I modified to look like this:

 SELECT DISTINCT
    sessions.user_id,
    DATEDIFF(sessions.created_at, user.created_at) AS DayOffset
    FROM sessions
    LEFT JOIN users ON (users.id = sessions.user_id)
    WHERE sessions.created_at >= CURDATE() - INTERVAL 6 DAY

I wanted the dayoffset not relative to the current date as in @Andriy M's answer, but relative to the date the user signed up. So I did left join on the user table to get the time the user signed up and did a date diff on that.

So the final query looks something like this:

SELECT u.DayOffset as Date,
  SUM(s.DayOffset = 0) AS d0,
  SUM(s.DayOffset = 1) AS d1,
  SUM(s.DayOffset = 2) AS d2,
  SUM(s.DayOffset = 3) AS d3,
  SUM(s.DayOffset = 4) AS d4,
  SUM(s.DayOffset = 5) AS d5,
  SUM(s.DayOffset = 6) AS d6
FROM (
 SELECT
    id,
    DATE(created_at) AS DayOffset
  FROM users
  WHERE created_at >= CURDATE() - INTERVAL 6 DAY
) as u
LEFT JOIN (
    SELECT DISTINCT
    sessions.user_id,
    DATEDIFF(sessions.created_at, user.created_at) AS DayOffset
    FROM sessions
    LEFT JOIN users ON (users.id = sessions.user_id)
    WHERE sessions.created_at >= CURDATE() - INTERVAL 6 DAY
) as s
ON s.user = u.id
GROUP BY u.DayOffset