Question

my SQL skills aren’t strong enough to figure this out, hope someone can help. This is on SQLite for Android:

I have a table ‘attempts’:

attempt_id | word | score | attempt_time
----------------------------------------
1          | w1   | 1     | 2011-09-01
2          | w1   | 2     | 2011-09-02
3          | w2   | 1     | 2011-09-02
4          | w3   | 1     | 2011-09-03
5          | w4   | 0     | 2011-09-03
6          | w1   | 0     | 2011-09-04

Each word has a score associated with it; I want to find the number of words that have a score >=1 for each day. Scores are preserved from day to do, so a score for day t should be reflected in day t+1. When a word goes to score 0, it should not be counted. The result should look something like this:

attempt_time | count(word)
--------------------------
2011-09-01   | 1              // w1 (1)
2011-09-02   | 2              // w1, w2 (2)
2011-09-03   | 3              // w1, w2, w3 (3)
2011-09-04   | 2              // w2, w3 (2) (w1 now has score 0)

There are lots of attempt_times, so you can’t loop through them individually. I suspect I need to use a subquery to sum the each date and the previous dates, but still need a way to discard duplicates (e.g. only count w1 once).

It should do something like this, but need all the dates rather than just one:

select count(distinct word) from attempts where score > 0 
and attempt_time <= '2011-09-03';

> 3

My alternative is to build a separate table that just keeps track of the totals on each day, but then I have to keep the data in sync.

Thanks much.

Edit: I’ve tried to add some more details to make the question more clear. Hope it helps.

Answer 1

It doesn’t seem like there’s a good way to do this.