Count occurences in Mysql - mysql

Question

Let's say, in given num_table, there is a column, in which only numbers from 1 to 35 are stored.
Code for count nums in last 25rows is:
select num, count(*)
from (select C_1 as num from num_table order by id desc limit 25) n
group by num
order by num asc;
Result:
| num | count(*) |
|------|----------|
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 2 |
| 10 | 1 |
| 11 | 1 |
| 12 | 1 |
| 15 | 1 |
| 16 | 2 |
| 17 | 1 |
| 20 | 1 |
| 21 | 1 |
| 22 | 1 |
| 23 | 1 |
| 25 | 1 |
| 28 | 2 |
| 29 | 2 |
| 30 | 1 |
| 32 | 2 |
|------|----------|
How to get a result, where nums from 1 to 35 - which occured 0 times within last 25 rows - will be also displayed?
Example of desired result:
| num | count(*) |
|------|----------|
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 2 |
| 6 | 0 |
| 7 | 0 |
| 8 | 0 |
| 9 | 0 |
| 10 | 1 |
| ... | ... |
| 35 | 0 |

Answer 1

Maybe the quickest way is to make your existing query as sub-query and LEFT JOIN your num_table with it like :
SELECT A.C_1, IFNULL(cnt,0) total_count
FROM num_table A
LEFT JOIN
(SELECT num, COUNT(*) cnt
FROM (SELECT C_1 AS num FROM num_table ORDER BY id DESC LIMIT 25) n
GROUP BY num) B
ON A.C_1=B.num
GROUP BY A.C_1, cnt
ORDER BY A.C_1 ASC;
Here's a fiddle for reference:
https://dbfiddle.uk/?rdbms=mysql_5.7&fiddle=3ced94d698fd8a55a8ad07a9d3b42f3d
And by the way, the current result you're showing is only 24 rows despite you did LIMIT 25 in the first sub-query. So in my example fiddle, the result is slightly different.

Answer 2

Here is another way to solve your problem.
In this solution, first, you need a table with numbers between 1 and 35, but only for the query, so then you can left join (because with a left join you can have also 0 counter values) it with your existent num_table.
You can do it like this:
WITH RECURSIVE numbers(id) AS (
SELECT 1 as id
UNION ALL
SELECT id+1 FROM numbers WHERE id < 35
)
SELECT numbers.id AS num, count(nt.id) AS total
FROM numbers
LEFT JOIN (SELECT C_1 FROM num_table ORDER BY id DESC LIMIT 25) nt ON (nt.C_1 = numbers.id)
GROUP BY numbers.id