Calculate read pages through select query in reading progress table - mysql

Question

I have a small program that I use to track my progress in reading books and stuff like goodreads to know how much I read per day.
I created two tables for that, tbl_materials(material_id int, name varchar), tbl_progress(date_of_update timestamp, material_id int foreign key, read_pages int, skipped bit).
Whenever I read some pages I insert into tbl_progress the current page that I've finished
I may read in the book multiple times. And if I skipped some pages I insert them into tbl_progress and mark the bit skipped to true. The problem is I can't query the tbl_progress to know how much I read per day
What I have tried is to find the last inserted progress for every single material in every single day
so for example:
+-------------+------------+---------+---------------------+
| material_id | read_pages | skipped | last_update |
+-------------+------------+---------+---------------------+
| 4 | 1 | | 2017-09-22 00:56:02 |
| 3 | 1 | | 2017-09-22 00:56:14 |
| 12 | 1 | | 2017-09-24 20:13:01 |
| 4 | 30 | | 2017-09-25 01:56:38 |
| 4 | 34 | | 2017-09-25 02:19:47 |
| 54 | 1 | | 2017-09-29 04:22:11 |
| 59 | 9 | | 2017-10-14 15:25:14 |
| 4 | 68 | T | 2017-10-18 02:33:04 |
| 4 | 72 | | 2017-10-18 03:50:51 |
| 2 | 3 | | 2017-10-18 15:02:46 |
| 2 | 5 | | 2017-10-18 15:10:46 |
| 4 | 82 | | 2017-10-18 16:18:03 |
| 4 | 84 | | 2017-10-20 18:06:40 |
| 4 | 87 | | 2017-10-20 19:11:07 |
| 4 | 103 | T | 2017-10-21 19:50:29 |
| 4 | 104 | | 2017-10-22 19:56:14 |
| 4 | 108 | | 2017-10-22 20:08:08 |
| 2 | 6 | | 2017-10-23 00:35:45 |
| 4 | 111 | | 2017-10-23 02:29:32 |
| 4 | 115 | | 2017-10-23 03:06:15 |
+-------------+------------+---------+---------------------+
I calculate my total read pages per day = last read page in this day - last read page in a date prior to this date and this works but the problem is I can't avoid skipped pages.
the first row in 2017-09-22 I read 1 page then another 1 page so the total read in this day = 2 (for only material_id = 4)
in 2017-09-25 the last update for material_id 4 is 34 pages which means I read 34-1 = 33 pages (last update in this day 34 - last update prior to this date 1) = 33
till now every thing works well but when it comes to considering skipped pages I could't do it for example:
in 2017-10-18 the last number of read pages for material_id = 4 was 34 (in 2017-09-25) then I skipped 34 pages and now the current page is 68 then read 4 pages (2017-10-18 03:50:51 ) then another 10 pages (2017-10-18 16:18:03) so the total for material_id = 4 is 14
I created a view to select the most recent last_update for every book in every day
create view v_mostRecentPerDay as
select material_id id,
(select title from materials where materials.material_id = id) title,
completed_pieces,
last_update,
date(last_update) dl,
skipped
from progresses
where last_update = (
select max(last_update)
from progresses s2
where s2.material_id = progresses.material_id
and date(s2.last_update) = date(progresses.last_update)
and s2.skipped = false
);
so if there are many updates for single book in one day, this view retrieves the last one (with the max of last_update) which accompany the biggest number of read pages and so for every single book
and another view to get the total read pages every day:
create view v_totalReadInDay as
select dl, sum(diff) totalReadsInThisDay
from (
select dl,
completed_pieces - ifnull((select completed_pieces
from progresses
where material_id = id
and date(progresses.last_update) < dl
ORDER BY last_update desc
limit 1
), 0) diff
from v_mostRecentPerDay
where skipped = false
) omda
group by dl;
but the problem is that the last view calculates skipped pages.
expected result:
+------------+------------------+
| day | total_read_pages |
+------------+------------------+
| 2017-09-22 | 2 |
+------------+------------------+
| 2017-09-24 | 1 |
+------------+------------------+
| 2017-09-25 | 33 |
+------------+------------------+
| 2017-09-29 | 1 |
+------------+------------------+
| 2017-10-14 | 9 |
+------------+------------------+
| 2017-10-18 | 19 |
+------------+------------------+
| 2017-10-20 | 5 |
+------------+------------------+
| 2017-10-21 | 0 |
+------------+------------------+
| 2017-10-22 | 21 |
+------------+------------------+
| 2017-10-23 | 8 |
+------------+------------------+
mysql> SELECT VERSION();
+-----------------------------+
| VERSION() |
+-----------------------------+
| 5.7.26-0ubuntu0.16.04.1-log |
+-----------------------------+

Answer 1

This seems like a super-convoluted way to evaluate pages read per day. Have you considered denormalising your data slightly and storing both the current page and the number of pages read?
The current page may make more sense stored in the material table, or in a separate bookmark table e.g.
bookmark - id, material_id, page_number
reading - id, bookmark_id, pages_complete, was_skipped, ended_at
When a reading (or skipping!) session is complete, the pages_complete can easily be calculated from the current page minus the old current page in the bookmark, and this can be done in your application logic
Your pages per day query simply becomes
SELECT SUM(pages_complete) pages_read
FROM reading
WHERE ended_at >= :day
AND ended_at < :day + INTERVAL 1 DAY
AND was_skipped IS NOT TRUE

Answer 2

You can make a view the uses the same columns of table progresses + another derived column which uses the same idea as #Arth suggested (pages_completed column)
This column will contain the current completed_pages - completed_pages with last update prior to the first completed pages which is the difference.
So for example if your progress table like this:
+-------------+------------+---------+---------------------+
| material_id | read_pages | skipped | last_update |
+-------------+------------+---------+---------------------+
| 4 | 68 | T | 2017-10-18 02:33:04 |
| 4 | 72 | | 2017-10-18 03:50:51 |
| 2 | 3 | | 2017-10-18 15:02:46 |
| 2 | 5 | | 2017-10-18 15:10:46 |
| 4 | 82 | | 2017-10-18 16:18:03 |
+-------------+------------+---------+---------------------+
we will add another derived column called diff.
where diff read_pages in 2017-10-18 02:33:04 - read_pages directly prior to 2017-10-18 02:33:04
+-------------+------------+---------+---------------------+------------------+
| material_id | read_pages | skipped | last_update | Derived_col_diff |
+-------------+------------+---------+---------------------+------------------+
| | 68 | T | 2017-10-18T02:33:04 | 68 - null = 0 |
| 4 | | | | |
+-------------+------------+---------+---------------------+------------------+
| 4 | 72 | | 2017-10-18T03:50:51 | 72 - 68 = 4 |
+-------------+------------+---------+---------------------+------------------+
| 2 | 3 | | 2017-10-18T15:02:46 | 3 - null = 0 |
+-------------+------------+---------+---------------------+------------------+
| 2 | 5 | | 2017-10-18T15:10:46 | 5 - 3 = 2 |
+-------------+------------+---------+---------------------+------------------+
| 4 | 82 | | 2017-10-18T16:18:03 | 82 - 72 = 10 |
+-------------+------------+---------+---------------------+------------------+
note: that 68 - null is null but I put it 0 for clarification
The derived column here is the difference between this read_pages - read_pages directly before this read_pages.
Here is a view
create view v_progesses_with_read_pages as
select s0.*,
completed_pieces - ifnull((select completed_pieces
from progresses s1
where s1.material_id = s0.material_id
and s1.last_update = (
select max(last_update)
FROM progresses s2
where s2.material_id = s1.material_id and s2.last_update < s0.last_update
)), 0) read_pages
from progresses s0;
Then you can select the sum of this derived column per day:
select date (last_update) dl, sum(read_pages) totalReadsInThisDay from v_progesses_with_read_pages where skipped = false group by dl;
Which will result in something like this:
+-------------+-----------------------------+
| material_id | totalReadsInThisDay |
+-------------+-----------------------------+
| 2017-10-18 | 16 |
+-------------+-----------------------------+
| 2017-10-19 | 20 (just for clarification) |
+-------------+-----------------------------+
Note that the last row is from my mind lol