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How to make left join and group by in linq?

I want to join 3 tables 2 of them inner join one of them left join after that i want to make group by. However, it gives an error. How can I handle that ?
this is code :
var people = from u in db.User.ToList()
join o in db.Offer.ToList() on u.UserId equals o.UserID where o.Statu == "Accepted"
join oz in db.log.ToList() on new { x1 = u.UserId.ToString(), x2 = o.CampaignId.ToString() } equals new { x1 = oz.ID, x2 = oz.CampaignID } into ps
from tbl in ps.DefaultIfEmpty()
group new { u, o, tbl } by new { u.UserId, o.CampaignId, o.Target, tbl.ID} into grp
select new { Username = grp.Key.UserId, CampaignID= grp.Key.CampaignId, Target = grp.Key.Target, id = grp.Key.ID};
Error occurs when i use tbl in group by. But i need to use it. I think some values comes null so it gives an error. How can i handle this ?

Translate nested select of oracle query to linq

I was given an oracle query and am trying to translate it to linq. I have been successful up to the point of the inner select.
select distinct pm.projNumber, nvl(s.submission_nbr, ppo.submission_nbr) submission_nbr, nvl(ot.objectname, pot.objectname) objectname , wa.assigned, f.lname, f.fname
from wfassignment wa
join CodeTab c on c.codeid = wa.appr_stat
join projobject po on po.objectid = wa.objectid
join projmain pm on pm.projid = po.projid
join hhistory s on s.Prop_no = pm.Prop_No and s.Inst_Code = pm.Inst_Code and pm.System = 'foo' and s.mark = po.mark
left join objecttypes ot on ot.objecttype = po.objecttype and ot.system = pm.system
left join(
select a.mark, a.objecttype, a.submitdate, c.submission_nbr
from projobject a
join b on b.projid = a.projid
join c on c.Prop_no = b.Prop_No and c.Inst_Code = b.Inst_Code and b.System = 'foo' and c.mark = a.mark ) ppo on ppo.mark = s.parentmark
left join objecttypes pot on pot.objecttype = ppo.objecttype and pot.system = pm.system
join faculty f on f.unique_id = wa.unique_id
where wa.completed is null and wa.unique_id in ('foo', 'bar', 'foo', 'bar')
below is my C# code up until "left join (select... )"
var pageObject = (
from wa in db.WFASSIGNMENTs
join c in db.CODETABs on wa.APPR_STAT equals c.CODEID
join po in db.PROJOBJECTs on wa.OBJECTID equals po.OBJECTID
join pm in db.PROJMAINs on po.PROJID equals pm.PROJID
join s in db.HHISTORies on new { pm.PROP_NO, pm.INST_CODE, po.MARK } equals new { s.PROP_NO, s.INST_CODE, s.MARK }
join ot in db.OBJECTTYPES on new { OBJECTTYPE = po.OBJECTTYPE, pm.SYSTEM } equals new { OBJECTTYPE = ot.OBJECTTYPE1, ot.SYSTEM }
How do I translate the inner select to linq?

I pulled out the inner select into another variable and just joined that variable. Did the trick.

Translate SQL statement with SUM() in Entity

I try to translate this SQL code :
SELECT w.Id, w.LastName, w.FirstName, SUM(d.Price*dt.Number) AS somme
FROM Waiter w
INNER JOIN Client c on w.Id = c.WaiterId
INNER JOIN DisheOnTable dt on c.Id = dt.ClientId
INNER JOIN Dishe d on dt.DisheId = d.Id
GROUP BY w.Id, w.LastName, w.FirstName
ORDER BY somme DESC;
in entity framework.
I tried something like this
var query2 = (from w in db.Waiter
join c in db.Client on w.Id equals c.WaiterId
join dt in db.DisheOnTable on c.Id equals dt.ClientId
join d in db.Dishe on dt.DisheId equals d.Id
group w by new { w.Id, w.LastName, w.FirstName } into g
//orderby g.Select() descending
select new
{
id = g.Key.Id,
lastname = g.Key.LastName,
firstname = g.Key.FirstName,
total = g.Sum(q => q.)
});
but my sum doesn't work (after multiple research and try) and i don't know how to multiply my variables.
PS : The SQL statement works well, i tried it.
Thank you for helping guys ! :)

You need to group on both dish and DishOnTable alias as Price is in Dish and Number is in DishOnTable:
group new{ d,dt} by new {w.Id, w.LastName, w.FirstName} into g
and now sum the columns which you want from it
select new {
id = g.Key.Id,
lastname = g.Key.LastName,
firstname = g.Key.FirstName,
total = g.Sum(q => q.d.Price * q.dt.Number)
}).OrderBy(x=>x.total)

linq to sql distinct values or group by

I have the folowing linq query.
How can I modify the query to return distinct values for CityFoo property only?
var query = from f in db.Foos
join b in db.Bars on f.IDFoo equals b.IDFoo
join fb in db.Fubars on b.IDBar equals fb.IDBar
select new MyViewModel {
IDFoo = f.IDFoo,
NameFoo = f.NameFoo,
CityFoo = f.CityFoo,
NameBar = b.NameBar,
NameFubar = fb.NameFubar };

I think you are missing information on your query.
If you want the first value to be used on the other properties, you need to tell that to Linq
So I am guessing that you actually want to group and then take the first.
Or...something like this:
var query = from f in db.Foos
join b in db.Bars on f.IDFoo equals b.IDFoo
join fb in db.Fubars on b.IDBar equals fb.IDBar
group new { f, b, fb } by f.CityFoo into grp
let first = grp.FirstOrDefault()
select new MyViewModel {
IDFoo = first.f.IDFoo,
NameFoo = first.f.NameFoo,
CityFoo = grp.Key,
NameBar = first.b.NameBar,
NameFubar = first.fb.NameFubar };

LINQ - multi join with Group by and get average

I'm trying to write this select in LINQ but Im not successful to fix it for long time. I also tried LINQ - join with Group By and get average but it doesn't work in my code. It is obviously that I'm wrong.
SQL:
SELECT name_type, AVG(t.price) as avgPrice FROM type tp
JOIN location l ON l.ID_type = tp.ID
JOIN event e ON e.ID_location = l.ID
JOIN ticket t ON t.ID_event = e.ID
GROUP BY tp.name_type
LINQ:
var q3 = from l in db.location
join tp in db.type on l.ID_type equals tp.ID
join e in db.event on l.ID equals u.ID_location
join t in db.ticket on e.ID equals t.ID_event
group tp by new {Type_name = tp.type_name} into grp
select new
{
Type_name = grp.Key.type_name,
avgPrice = grp.Average( x => x.ticket.price)
};

There are a few problems:
There is an error in the second join—I believe u.ID_location needs to be e.ID_location.
I think you are grouping on the wrong entity, try grouping by t instead of tp.
You don't need the anonymous type in the group by.
Try this:
var results =
from l in db.location
join tp in db.type on l.ID_type equals tp.ID
join e in db.event on l.ID equals e.ID_location
join t in db.ticket on e.ID equals t.ID_event
group t by new tp.type_name into grp
select new
{
Type_name = grp.Key,
avgPrice = grp.Average(x => x.price)
};
If you happen to have navigation properties set up between your entities, this would be a lot easier. It's pretty hard to tell how the entities are supposed to be related, but I'm thinking something like this would work:
// average ticket price per location type
var results =
from t in db.ticket
group t by t.event.location.type.type_name into g
select new
{
Type_name = g.Key,
avgPrice = g.Average(x => x.price)
};
Or in fluent syntax:
var results = db.ticket.GroupBy(t => t.event.location.type.type_name)
.Select(g => new
{
Type_name = g.Key,
avgPrice = g.Average(x => x.price)
});