Query to select value from another table as a column - mysql

Question

I have a query to report some data :
select r.m_id,
count(distinct case when r.sal = '1val' then r.login end) as 1val,
count(distinct case when r.sal = '2val' then r.login end) as 2val,
count(distinct case when r.sal = '3val' then r.login end) as 3val,
...
from read_log r
inner join mes m on m.id = r.m_id
where
YEAR(m.send_date) = YEAR(curdate())
group by r.m_id
r.sal value in count(distinct case when r.sal = '1val' then r.login end) as 1val only changes. Finally it shows results in each column for every r.sal. There are currently over 80 diffrent r.sal and its growing.
My question is:
It is possible to take value for r.sal from another table?
Like new table sal with this 1val, 2val, 3val, 4val, 5val etc...?
Maybe loop or something like that:
count(distinct case when r.sal = (select val from sal) then r.login end)
(I know its wrong but maybe it will illustrate it better)
count(distinct case... is great to show data for each r.sal value in the other column but maybe is another way to achieve that...

Answer 1

CREATE TABLE sal_table (sal CHAR(4));
INSERT INTO sal_table VALUES ('1val'), ('2val'), ... ;
CREATE PROCEDURE get_data ()
BEGIN
SELECT CONCAT (
'select r.m_id, ',
GROUP_CONCAT(
CONCAT(
'count(distinct case when r.sal = ''',
sal,
''' then r.login end) as `',
sal,
'`'
)
),
' from read_log r ',
'inner join mes m on m.id = r.m_id ',
'where YEAR(m.send_date) = YEAR(curdate()) ',
'group by r.m_id'
)
INTO #sql
FROM sal_table;
PREPARE stmt FROM #sql;
EXECUTE stmt;
DROP PREPARE stmt;
END
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=af55c52aca3280410fba1f3a453aab09
PS. Recommended edition: WHERE m.send_date >= DATE_FORMAT(CURRENT_DATE, '%Y-01-01') AND m.send_date < DATE_FORMAT(CURRENT_DATE + INTERVAL 1 YEAR, '%Y-01-01'). Such condition is sargable rather than your one.