Question

I have the following data in my table. BTW … this is a DD/MM/YYYY format:

Date
18/09/2012
17/09/2012
13/09/2012
11/09/2012
10/09/2012
09/09/2012
25/08/2012
24/08/2012

The result what I want are:

Date
18/09/2012
13/09/2012
11/09/2012
09/09/2012
25/08/2012

The rule:
It starts from the latest date (18/09/2012) and check the next one down (17/09/2012). If there is a date then removed that from the list because it requires to have 1 day apart. Then goes to 13/09/2012 and then check 12/09/2012 and didn’t find and then move to next one so on and so on. Basically you can’t have date close each other (min 1 day apart).

Now I can do this on cursor if it’s on TSQL however since I’m working on MySQL, is there any such thing in MySQL? Or perhaps any sub-queries approach that can solve this query?

I’m appreciated your feedback.

Answer 1

Try this solution –

SELECT date FROM (
  SELECT
    date, @d := IF(@d IS NULL OR DATEDIFF(@d, date) > 1, date, @d) start_date
  FROM
    dates,
   (SELECT @d:=null) t
  ORDER BY
    date DESC
) t
WHERE start_date = date

The subquery finds out start days (18, 13, 11…), then WHERE condition filters records. Try to run the subquery to understand how it works –

  SELECT
    date, @d := IF(@d IS NULL OR DATEDIFF(@d, date) > 1, date, @d) start_date
  FROM
    dates,
   (SELECT @d:=null) t
  ORDER BY
    date DESC