how to combine sql statement to get it in one

Question

SELECT mem_id, sum(commission)
FROM `member_commission`
group by mem_id

SELECT mem_id, sum(crowdfund)
FROM `crowdfund`
group by mem_id

i want to combine both of these commands in one and then group them by mem_id

+

both of my table (member_commission, crowd fund) have a (datetime stamp - which records date and time) column which is time column present in membecommission and distrbutedmonth in crowdfund.... and i just want the result of the present month only...

the datetime column records date and time in this format : 2018-08-22 22:02:09

Answer 1

One method uses union all and group by :

select mem_id, sum(commission), sum(crowdfund)
from ((select mc.mem_id, mc.commission, 0 as crowdfund
       from member_commission mc
      ) union all
      (select cf.mem_id, 0, cf.crowdfund
       from crowdfund cf
      )
     ) x
group by mem_id;

This is tricky because members could be in either table -- and presumably you still want them in the result set.