Question

Tables:

- Activities: id, userId, description, buildingId
- Buildings: id, name
- User: id, name, gender

Users can create activities for example: “checking mail” would be an activity, the buildingid links to a building where a certant activity is going on.

What I need is a query that will get the % male/female per building, based of the amount of activities going on at such building.

For example:

User: 1, mike
Building: 1, main hall

Activities:

id: 1
userId: 1 (mike)
description: "checking mail"
buildingId: 1 (main hall)

id: 2
userId: 1 (mike)
description: "getting coffee"
buildingId: 1 (main hall)

So I want to get the % female / male of the building 1 (main hall) how can I do this the best way?

Answer 1

SELECT buildingId, 
  (SUM(CASE WHEN `User`.gender='male' THEN 1 ELSE 0 END)/
  COUNT(*))*100 as male_percent
FROM Activities JOIN `User` ON Activities.userID=`User`.id 
GROUP BY `Activities`.buildingId

Or if you prefer ratio:

SELECT buildingId, 
  SUM(CASE WHEN `User`.gender='male' THEN 1 ELSE 0 END)/
  SUM(CASE WHEN `User`.gender='female' THEN 1 ELSE 0 END) as ratio
FROM Activities JOIN `User` ON Activities.userID=`User`.id 
GROUP BY `Activities`.buildingId