Question

I need to write a query that displays, for each activity, a count of the number of males and number of females.

Preferably in a 3 column format, activity_name, male (computed column), female (computed column).

I think I may need to use nested queries, but I cannot figure out how. Or could this be done by just using GROUP BY?

My tables are:

Child
child_id
child_fname
child_sname
child_gender
etc etc

Activity
activity_id
activity_name
etc etc

Child_Activity_Item
child_id
activity_id

Thank you

Answer 1

Try this query –

SELECT
  a.activity_id,
  a.activity_name,
  COUNT(IF(c.child_gender = 'M', c.child_gender, NULL)) male,
  COUNT(IF(c.child_gender = 'F', c.child_gender, NULL)) female
FROM
  Activity a
  JOIN Child_Activity_Item ca
    ON ca.activity_id = a.activity_id
  JOIN Child c
    ON c.child_id = ca.child_id
GROUP BY a.activity_id