Time series group by day and kind - sql

Question

I create a table using the command below:
CREATE TABLE IF NOT EXISTS stats (
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
session_kind INTEGER NOT NULL,
ts TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
)
I insert some time series data using the command below:
INSERT INTO stats (session_kind) values (?1)
Some time after having executed several times the insert command, I have some time series data as below:
id session_kind ts
-----------------------------------------
1 0 2020-04-18 12:59:51 // day 1
2 1 2020-04-19 12:59:52 // day 2
3 0 2020-04-19 12:59:53
4 1 2020-04-19 12:59:54
5 0 2020-04-19 12:59:55
6 2 2020-04-19 12:59:56
7 2 2020-04-19 12:59:57
8 2 2020-04-19 12:59:58
9 2 2020-04-19 12:59:59
10 0 2020-04-20 12:59:51 // day 3
11 1 2020-04-20 12:59:52
12 0 2020-04-20 12:59:53
13 1 2020-04-20 12:59:54
14 0 2020-04-20 12:59:55
15 2 2020-04-20 12:59:56
16 2 2020-04-20 12:59:57
17 2 2020-04-20 12:59:58
18 2 2020-04-21 12:59:59 // day 4
What I would like to have a command that groups my data by date from the most recent day to the least and the number of each session_kind like below (I don't want to give any parameter to this command):
0 1 2 ts
-------------------------
0 0 1 2020-04-21 // day 4
3 2 3 2020-04-20 // day 3
2 2 4 2020-04-19 // day 2
1 0 0 2020-04-18 // day 1
How can I group my data as above?

Answer 1

You can do conditional aggregation:
select
sum(session_kind= 0) session_kind_0,
sum(session_kind= 1) session_kind_1,
sum(session_kind= 2) session_kind_2,
date(ts) ts_day
from mytable
group by date(ts)
order by ts_day desc
If you want something dynamic, then it might be simpler to put the results in rows rather than columns:
select date(ts) ts_day, session_kind, count(*) cnt
from mytable
group by date(ts), session_kind
order by ts_day desc, session_kind

Answer 2

If I understand correctly, you just want to sum the values:
select date(timestamp),
sum(case when session_kind = 1 then 1 else 0 end) as cnt_1,
sum(case when session_kind = 2 then 1 else 0 end) as cnt_2,
sum(case when session_kind = 3 then 1 else 0 end) as cnt_3
from t
group by date(timestamp);
You can also simplify this:
select date(timestamp),
sum( session_kind = 1 ) as cnt_1,
sum( session_kind = 2 ) as cnt_2,
sum( session_kind = 3 ) as cnt_3
from t
group by date(timestamp);