mysql various group by in one query - mysql

Question

I would like to get statistics on my dataset,
for example this is my dataset:
FirstName LastName Country City BirthMonth
Donald Trump England London Jan
Bill Gates England London Sep
Donald Suther England York Sep
Donald Suther Germany Berlin Jan
and this is my 'group_by' list:
[['FirstName', 'LastName'], ['Country', 'City'], ['BirthMonth']]
I would like to get the following statistics:
group by FirstName & LastName:
FirstName LastName Count
Donald Trump 1
Donald Suther 2
Bill Gates 1
group by Country & City:
Country City Count
England London 2
England York 1
Germany Berlin 1
group by BirthMonth:
BirthMonth Count
Jan 2
Sep 2
my query would look like this:
select FirstName, LastName, Country, City, BirthMonth
from my_table
where <some conditions to filter rows only from certain timestamp>
now I have two options:
a. return all values to server and process there (I'm using python) - this query includes many rows and causes overhead
b. query multiple times, each time grouping by the specific fields
select FirstName, LastName, count(*) as group_by
from my_table
where ...
group by FirstName, LastName
c. is there a third option of having one query, and return all different 'group_by's?
and another question:
from (a) and (b) which is better?
I'll note that the group by has limited options - for example 'FirstName' has only 20 options, this means that (b) will result each time less than 20*(num of group by in query rows) < 40, but (a) will result 20^5 rows which is tons of data
to simplify I'll assume there aren't more than 2 columns in a group_by each time,
(which is actually the current situation, it might grow in the future but currently I can use a solution that takes that into account)

Answer 1

You can combine each grouped query with the others using UNION. Fill in the unused columns in each subquery with NULL.
SELECT FirstName, LastName, NULL AS Country, NULL AS City, NULL AS BirthMonth, COUNT(*) AS count
FROM my_table
GROUP BY FirstName, LastName
UNION ALL
SELECT NULL, NULL, Country, City, NULL, COUNT(*)
FROM my_table
GROUP BY Country, City
UNION ALL
SELECT NULL, NULL, NULL, NULL, BirthMonth, COUNT(*)
FROM my_table
GROUP BY BirthMonth