Question

I have 4 tables: users, userpreference, userinfo, useredu

the last three tables use “id” as a foreign key referencing the table ‘users’ :

Query to be formulated:

i need to find the “top music among all single females who go to MSU”

noting that MSU could also be ‘Minnesota State University”

i have this query so far but it is not producing the correct results?

select userpreference.preferencevalue as 'Music', COUNT(*) as 'SingleFemaleCount'from users, userpreference, userinformation
where users.Id = userinformation.Id
and users.Id = userpreference.Id
and userpreference.Id = userinformation.Id
and users.Gender = 'female'
and userinformation.informationvalue = 'single'
and usereducation.school like 'msu%' OR like 'minnesota state%'
and userpreference.preferencetype = 'music' GROUP BY preferencevalue ORDER BY      COUNT(distinct users.Id) DESC limit 10

Answer 1

It might be as simple as you need some parenthesis in your where clause:

(usereducation.school like 'msu%' OR like 'minnesota state%')

Otherwise, the OR will be of lower precedence than the adjacent ANDs.

EDIT: 2011-03-06

Below, I have formatted the code to make it a little easier to read, and also moved the userinformation and usereducation checking into exists() clauses. The reason I am doing this is because if a user has more than 1 userinformation or usereductionat row matching your criteria, it would affect the count() aggregate.

select
    userpreference.preferencevalue as 'Music',
    COUNT(*) as 'SingleFemaleCount'

from users, userpreference
where users.Gender = 'female'
  and userpreference.Id = users.Id
  and userpreference.preferencetype = 'music'

  and exists
    (select *
    from userinformation
    where userinformation.Id = users.Id
      and userinformation.informationvalue = 'single')

  and exists
    (select *
    from usereducation
    where usereducation.Id = users.Id
      and (usereducation.school like 'msu%' OR like 'minnesota state%'))

GROUP BY userpreference.preferencevalue
ORDER BY COUNT(*) DESC limit 10

Another thing to check is that (usereducation.school like 'msu%' OR like 'minnesota state%') indeed finds all MSU records. If the result set is not too huge, would run a select distinct school from usereducation to check and see that sure you are getting all records.

Lastly, I sort of prefer to use the join syntax as follows:

select
    userpreference.preferencevalue as 'Music',
    COUNT(*) as 'SingleFemaleCount'

from users
inner join userpreference on userpreference.Id = users.Id
where users.Gender = 'female'
  and userpreference.preferencetype = 'music'

  and exists
    (select *
    from userinformation
    where userinformation.Id = users.Id
      and userinformation.informationvalue = 'single')

  and exists
    (select *
    from usereducation
    where usereducation.Id = users.Id
      and (usereducation.school like 'msu%' OR like 'minnesota state%'))

GROUP BY userpreference.preferencevalue
ORDER BY COUNT(*) DESC limit 10

I realize I totally changed your query, but hey this is homework, right 🙂