SQL query help

Question

Hi, I wrote a query

select u.user, g.group, u2g.something 
from   users, groups, u2g 
where  users.u = u2g.u and groups.g = u2g.g

that returns data like this:

user, group, something
----------------------
1   , 3,     a
1   , 5,     b
2   , 3,     c
3   , 3,     d
4   , 5,     e

now I would like to limit this query in such a way that it only shows users which are both in groups 3 and 5 - so it would only return {1,3, a} , {1,5, b} for my example data.

edit: I added another column to the data because there may be an incorrect solution using a group by.

edit2: sorry, I was misled by documentation. MySQL 4.0 does not support subqueries :(

edit3: This SQL will be generated programatically for any number of groups (well, up to 20 in current specification) so I would like to avoid solutions that give me too much additional coding to do. If a solution will not be found, I will just modify the resulting .Net 1.1 DataTable, but I would like to avoid that if possible.

edit4: any new idea? Perhaps one without subqueries that includes IN (3,5)?

Answer 1

Its not and answer to your question but why don't you use Joins?

Answer 2

select u.user, g.group, u2g.something 
from users u, groups g, u2g 
where u.user = u2g.user and g.group = u2g.group 
    where exists 
     (select 1 
         from u2g u2g2 
        where u2g2.user=u.user and u2g2.group in(3,5))

Answer 3

Something along these lines?

select u.[user], g.group
from     u
    inner join ug on ug.userid = u.id 
    inner join g on g.id = ug.groupid
    inner join 
    (
     select ug.userid
     from ug
     where ug.groupid in (1,2)
     group by ug.userid
     having count(*) = 2
    ) sub on sub.userid = u.id

-Edoode

Answer 4

Using double join with groups-table will give you the correct result:

  select u.user, u2g.something 
  from   users 
  INNER JOIN u2g ON users.u = u2g.u
  INNER JOIN groups g1 ON u2g.g = g1.g AND g1.group = 3
  INNER JOIN groups g2 ON u2g.g = g2.g AND g2.group = 5
  /* try this for two rows, one for each group */
  INNER JOIN groups ON u2g.g = groups.g

However, this doesn't exactly match your request, that you want two rows, one for each group. This will only give you one row, you might be able to join it once more with groups therefor rendering two rows.

Another example (if you're selecting using the same groupID that you map against ):

SELECT u.uID, gm.something 
FROM cdcms_users u 
inner join cdcms_group_memberships gm1 on gm1.uID = u.uID AND gm1.gID = 32
inner join cdcms_group_memberships gm2 on gm2.uID = u.uID AND gm2.gID = 33

Answer 5

Quite hideous non-general solution that results in two rows in Oracle:

  select users.u, groups.g
    from   users , groups, u2g, groups g2, u2g u2g2
    where  users.u = u2g.u 
           and users.u = u2g2.u
           and groups.g = u2g.g
           and g2.g = u2g2.g
           and (groups.g in (3,5) and g2.g in (3,5) and groups.g <> g2.g)
           ;

Answer 6

Why is groups used in the query? Its only accessed field (g) exists in u2g. I imagine you probably want to bring back a boatload of stuff from there as well.

In order to get the sort of resultset you describe without the use of subqueries you end up with a real mess: a quadratic explosion of query text!

You'll need something of the following form:

select users.u, groups.g, u2g0.something
from users u, groups g, u2g u2g0, u2g u2g1
where groups.g = 3
     and users.u = u2g0.u
     and u2g0.g = 3
     and users.u = u2g1.u
     and u2g1.g = 5
union all
select users.u, groups.g, u2g1.something
from users u, groups g, u2g u2g0, u2g u2g1
where groups.g = 5
     and users.u = u2g0.u
     and u2g0.g = 3
     and users.u = u2g1.u
     and u2g1.g = 5

Since this is a programmatically generated query, I'll use a web-page-scripting-like notation here to describe the query construction. I will also make the rash and unwarranted simplifying assumption that the group identifiers are not a potential SQL-injection attack vector. :-)

<% for(int i = 0; i < requiredGroups.Length; i++) { %>
  <% if(i > 0) { %>
    union all
  <% } %>
select users.u, groups.g, u2g<%=i%>.something
from users u, groups g
  <% for(int j = 0; j < requiredGroups.Length; j++) { %>
     , u2g u2g<%=j%>
  <% } %>
where groups.g = <%=requiredGroups[i]%>
  <% for(int j = 0; j < requiredGroups.Length; j++) { %>
     and users.u = u2g<%=j%>.u
     and u2g<%=j>.g = <%=requiredGroups[j]%>
  <% } %>
<% } %>