MySQL查询联接3个表并计数

Question

I've been stuck on this problem for far too long.
I have to merge 3 tables and do some counting of distinct values.
I have 3 tables
1.User_me
profileId( String )
responded( int 1 or 0)

2.Profiles
profileId ( String )
idLocation ( int )

3.lookup_location
id ( int )
location (String )

I can join User_me and Profiles ON User_me.profileId = Profiles.profileId
I can join Profiles and lookup_location ON Profiles.idLocation = lookup_location.id

Under Profiles I need to count the number of distinct values for idLocation where User_me.profileId = Profiles.profileId
I also need to count the number of Profiles.idLocation that have User_me.responded = 1

I have this:

SELECT lookup.location, count(*) as total
FROM User_me user
JOIN Profiles
  ON user.profileId= profiles.profileId
JOIN lookup_location lookup
  ON profiles.idLocation = lookup.id
GROUP BY profiles.idLocation

but I still need to have the column giving me the count where User_me.responded = 1
Something like:

SELECT lookup.location, count(*) as total, count(*) responded

Answer 1

If I'm understanding your question correctly, you can you a case statement in the count aggregate:

SELECT lookup.location, count(*) as total, 
    count(case when user.responded = 1 then 1 end) as responded
FROM User_me user
JOIN Profiles
  ON user.profileId= profiles.profileId
JOIN lookup_location lookup
  ON profiles.idLocation = lookup.id
GROUP BY profiles.idLocation

Since you're using MySQL , you can also use something like sum(user.responded = 1) .