Select less nearest date from table [group by and order by] - mysql

Question

I'm trying to find the nearest date for each group Type, Subtype, s_stype, category_id. If there is no date found take a with default value:
Sample data :
Type
subtype
s_stype
category_Id
date
1
1
1
211
20000000
1
1
1
211
30000000
1
1
2
211
20000000
1
1
2
211
20000000
1
1
3
211
null
1
1
2
311
50000000
1
1
2
311
40000000
1
1
2
311
null
Query:
Select *
from Table
where date <= input_date or date is null
group by Type, Subtype, s_stype, category_id
order by date desc
The query should take less nearest date for each type, subtype, s_stype, category.
For example, given input_date = 25000000:
Type
subtype
s_stype
category_Id
date
1
1
1
211
20000000
1
1
2
211
20000000
1
1
3
211
null
1
1
2
311
null
the query should give above result instead it gives incorrect row that takes a first row which satisfy where condition of given group criteria
As i have used mysql 5.7 so i need solution without window functions solution like the above

Answer 1

Getting the best row per group means there does not exist a better row for the group. And "closer" means that the absolute value of the difference of the two dates is smaller. This is how my query below works.
As your dates in your example are integers, I am showing integer math here. If you are working with real dates, you must use DATEDIFF instead of subtraction, because MySQL has a flaw concerning this allowing subtracting one date from another but returning some number that doesn't seem to have a meaning instead of returning an interval or a value of a predefined unit such as dates.
select *
from mytable
where not exists
(
select null
from mytable better
where better.type = mytable.type
and better.subtype = mytable.subtype
and better.s_stype = mytable.s_stype
and better.category_id = mytable.category_id
and
(
abs(better.date - 25000000) < abs(mytable.date - 25000000)
or
(better.date is not null and mytable.date is null)
)
)
order by type, subtype, s_stype, category_id, date;