CODEWITHSUNDEEP
phpmysqlsql
Harea Costicla
Harea Costicla

Reputation: 817

Get sql by consecutive hours

I have a question. Suppose I have this table in SQL:

date                        user_id             
2015-03-17 00:06:12         143
2015-03-17 01:06:12         143
2015-03-17 02:06:12         143
2015-03-17 09:06:12         143
2015-03-17 10:10:10         200

I want to get the number of consecutive hours. For example, for user 143, I want to get 2 hours, for user 200 0 hours. I tried like this :

select user_id, TIMESTAMPDIFF(HOUR,min(date), max(date)) as hours
from myTable
group by user_id

But this query fetches all non-consecutive hours. Is it possible to solve the problem with a query, or do I need to post-process the results in PHP?

Upvotes: 2

Views: 264

Answers (2)

Ruslan Osmanov
Ruslan Osmanov

Reputation: 21492

Another version using temporary variables:

SET @u := 0;
SET @pt := 0;
SET @s := 0;

SELECT `user_id`, MAX(`s`) `conseq` FROM
(
  SELECT
  @s := IF(@u = `user_id`,
    IF(UNIX_TIMESTAMP(`date`) - @pt = 3600, @s + 1, @s),
      0) s,
  @u := `user_id` `user_id`,
  @pt := UNIX_TIMESTAMP(`date`) pt
  FROM `users`
  ORDER BY `date`
) AS t
GROUP BY `user_id`

The subquery sorts the rows by date, then compares user_id with the previous value. If user IDs are equal, calculates the difference between date and the previous timestamp @pt. If the difference is an hour (3600 seconds), then the @s counter is incremented by one. Otherwise, the counter is reset to 0:

s user_id pt
0 143     1426529172
1 143     1426532772
2 143     1426536372
2 143     1426561572
0 200     1426565410

The outer query collects the maximum counter values per user_id, since the maximum counter value corresponds to the last counter value per user_id.

Output

user_id conseq
143     2
200     0

Note, the query accepts the difference of exactly 1 hour. If you want a more flexible condition, simply adjust the comparison. For example, you can accept a difference in interval between 3000 and 4000 seconds as follows:

  @s := IF(@u = `user_id`,
    IF( (UNIX_TIMESTAMP(`date`) - @pt) BETWEEN 3000 AND 4000, @s + 1, @s),
      0) s

Upvotes: 1

fancyPants
fancyPants

Reputation: 51868

Use a variable to compare with the previous row. 

SELECT user_id, SUM(cont_hour) FROM (
    SELECT
    user_id,
    IF(CONCAT(DATE(@prev_date), ' ', HOUR(@prev_date), ':00:00') - INTERVAL 1 HOUR = CONCAT(DATE(t.date), ' ', HOUR(t.date), ':00:00')
AND @prev_user = t.user_id, 1, 0) AS cont_hour
    , @prev_date := t.date
    , @prev_user := t.user_id
    FROM
    table t
    , (SELECT @prev_date := NULL, @prev_user := NULL) var_init_subquery
    WHERE t.date BETWEEN <this> AND <that>
    ORDER BY t.date
) sq
GROUP BY user_id;

I made the comparison a bit more complicated than you expected, but I thought it's necessary, that you don't just compare the hour, but also, that it's the same date (or the previous day, when it's around midnight).

  • you can read more about user variables here

As a short explanation: The ORDER BY is very important, as well as the order in the SELECT clause. The @prev_date holds the "previous row", cause we assign the value of the current row after we made our comparison.

Upvotes: 2

Related Questions