Query with group by date - mysql

Question

I'm working on the following user table, where role = 2 means the user is an instructor, and role = 3 means that the user is a student.
+--------+------+---------------+
| name | role | creation_date |
+--------+------+---------------+
| Tom | 2 | 2020-07-01 |
| Diana | 3 | 2020-07-01 |
| Rachel | 3 | 2020-07-01 |
| Michel | 3 | 2020-08-01 |
+--------+------+---------------+
My goal is to select the sum value of all instructors and students, grouped by date. The result should look like this:
+------------------+---------------+---------------+
| totalInstructors | totalStudents | creation_date |
+------------------+---------------+---------------+
| 1 | 2 | 2020-07-01 |
| 0 | 1 | 2020-08-01 |
+------------------+---------------+---------------+
In this case, on 2020-07-01, I had 1 instructor and 2 students registered and on 2020-08-01, I had no instructors and I had 1 student registered.
My problem is that I am having difficulties in setting up this query, if someone can help me thank you very much!

Answer 1

You would need count with a case statement as follows
select count(case when role=2 then 1 end) as totalInstructors
,count(case when role=3 then 1 end) as totalStudents
,creation_date
from tbl
group by creation_date

Answer 2

Use conditional aggregation:
SELECT
creation_date,
COUNT(CASE WHEN role = 2 THEN 1 END) AS totalInstructors,
COUNT(CASE WHEN role = 3 THEN 1 END) AS totalStudents
FROM yourTable
GROUP BY
creation_date;
Demo

Answer 3

A simple GRoupBY and SUM helps
This works. because the compasison role = 2 gives 1 back it it tue and 0 if it is false
CREATE TABLE table1 (
`name` VARCHAR(6),
`role` INTEGER,
`creation_date` VARCHAR(10)
);
INSERT INTO table1
(`name`, `role`, `creation_date`)
VALUES
('Tom', '2', '2020-07-01'),
('Diana', '3', '2020-07-01'),
('Rachel', '3', '2020-07-01'),
('Michel', '3', '2020-08-01');
SELECT
SUM(`role` = 2) totalInstructors ,
SUM(`role` = 3) totalStudents,
`creation_date`
FROM table1
GROUP BY `creation_date`
ORDER BY `creation_date`
totalInstructors | totalStudents | creation_date
---------------: | ------------: | :------------
1 | 2 | 2020-07-01
0 | 1 | 2020-08-01
db<>fiddle here

Answer 4

Please use below query,
select
case when role = 2 then count(1) end as totalInstructors,
case when role = 3 then count(1) end as totalStudents,
creation_date
from table_name
group by creation_date;
You can use COALESCE() to replace null with 0
select COALESCE(totalInstructors, 0) as totalInstructors, COALESCE(totalStudents, 0) as totalStudents,creation_date
from
(select
case when role = 2 then count(1) end as totalInstructors,
case when role = 3 then count(1) end as totalStudents,
creation_date
from table_name
group by creation_date) qry;