I have an oracle database design as shown in the picture.
my question, how can i display id_produk of tb_produk by using select with condition :
produk_gaya.id_ghidup = wajah_gaya.id_ghidup
produk_konsern.id_konsern = wajah_konsern.id_konsern
produk_tipe.id_tipe = tb_wajah.id_tipe
Please help, thank you
image of database design
You appear to just want to join the tables along the primary and foreign key relationships (you can skip tb_hidup as produk_gaya and wajah_gaya both have foreign-key relationship to the same primary key; similar for tb_konsern and tb_type):
SELECT p.id_produk
FROM tb_produk p
INNER JOIN produk_gaya pg ON p.id_produk = pg.id_produk
INNER JOIN wajah_gaya wg ON pg.id_ghidup = wg.id_ghidup
INNER JOIN produk_konsern pk ON p.id_produk = pk.id_produk
INNER JOIN wajah_konsern wk ON pk.id_konsern = wk.id_konsern
INNER JOIN produk_tipe pt ON p.id_produk = pt.id_produk
INNER JOIN tb_wajah w ON pt.id_tipe = tb_wajah.id_tipe
I have the following query in one of my Entity Framework Core API controllers:
var plotData = await (from nl in _context.BookList
join ql in _context.PlotList on nl.PlotId equals ql.PlotId
join qc in _context.PlotChoices on ql.PlotId equals qc.PlotId
join nk in _context.BookLinks.DefaultIfEmpty() on qc.ChoiceId equals nk.ChoiceId
where nl.Id == ID
select new
{ .. }
I need it to return all rows even if data doesn't exist in the BookLinks table.
However, it's not returning rows if there is no data data in the BookLinks table for that row.
But this SQL query, from which I'm trying to model from, does return data...it returns nulls if there is no data in BookLinks.
select * from BookList bl
left join PlotList pl ON bl.plotId = bl.plotId
left join PlotChoices pc ON pl.plotId = pc.plotId
left join BookLinks bk ON pc.choiceID = bk.choiceID
where nl.caseID = '2abv1'
From what I read online, adding 'DefaultIfEmpty()' to the end of BookLinks should fix that, but it hasn't.
What am I doing wrong?
Thanks!
When using left join , you can try below code sample :
var plotData = (from nl in _context.BookList
join ql in _context.PlotList on nl.PlotId equals ql.PlotId
join qc in _context.PlotChoices on ql.PlotId equals qc.PlotId
join nk in _context.BookLinks on qc.ChoiceId equals nk.ChoiceId into Details
from m in Details.DefaultIfEmpty()
where nl.Id == ID
select new
{
}).ToList();
I've this query that i'm trying to put as linq:
select *
from stuff
inner join stuffowner so on so.stuffID = stuff.stuffID
left outer join (select min(loanId) as loanId, stuffownerId from loan
where userid = 1 and status <> 2 group by stuffownerId) t on t.stuffownerid = so.stuffownerid
left outer join loan on t.LoanId = loan.LoanId
when this is done, I would like to do a linq Group by to have Stuff has key, then stuffowners + Loan as value.
I can't seem to get to a nice query without sub query (hence the double left outer).
So basically what my query does, is for each stuff I've in my database, bring the owners, and then i want to bring the first loan a user has made on that stuff.
I've tried various linq:
from stuff in Stuffs
join so in StuffOwners on stuff.StuffId equals so.StuffId
join tLoan in Loans on so.StuffOwnerId equals tLoan.StuffOwnerId into tmpJoin
from tTmpJoin in tmpJoin.DefaultIfEmpty()
group tTmpJoin by new {stuff} into grouped
select new {grouped, fluk = (int?)grouped.Max(w=> w.Status )}
This is not good because if I don't get stuff owner and on top of that it seems to generate a lot of queries (LinqPad)
from stuff in Stuffs
join so in StuffOwners on stuff.StuffId equals so.StuffId
join tmpLoan in
(from tLoan in Loans group tLoan by tLoan.StuffOwnerId into g
select new {StuffOwnerId = g.Key, loanid = (from t2 in g select t2.LoanId).Max()})
on so.StuffOwnerId equals tmpLoan.StuffOwnerId
into tmptmp from tMaxLoan in tmptmp.DefaultIfEmpty()
select new {stuff, so, tmptmp}
Seems to generate a lot of subqueries as well.
I've tried the let keyworkd with:
from tstuffOwner in StuffOwners
let tloan = Loans.Where(p2 => tstuffOwner.StuffOwnerId == p2.StuffOwnerId).FirstOrDefault()
select new { qsdq = tstuffOwner, qsdsq= (int?) tloan.Status, kwk= (int?) tloan.UserId, kiwk= tloan.ReturnDate }
but the more info i get from tLoan, the longer the query gets with more subqueries
What would be the best way to achieve this?
Thanks
I want to join the following Tables
1. B_Book[1st Table]
-B_BID (Book ID)(PK)
-B_Name
-B_CategroyID (FK)
2. BI_BookInstance [2nd Table]
-BI_IID(Instance ID)
-BI_BID (FK)
-BI_Price
3. BC_BookCategory [3rd Table]
-BC_CategoryID (PK)
-BC_CategoryName
First Join B_Book and BI_BookInstance then join the result of those both with BookCategory.
(1st join)[B_BID equals BI_BID]
(2nd nested join)[result of 1st join B_CategoryID equals BC_CategoryID]
Edit
SQL would be something like the following:
SELECT * FROM
(SELECT * FROM B_Book b JOIN BI_BookInstance bi on b.B_BID = bi.BI_BID) as t1
JOIN BC_BookCategoryID bc on bc.BC_CategoryID = t1.B_CategoryID
What matches your query in LINQ would be the following (and you'll notice the similarity with SQL). I've also included some examples on how to rename the fields returned, such as Price or CategoryName:
var results = from b in B_Book
join bi in BI_BookInstance
on b.B_BID equals bi.BI_BID
join bc in BC_BookCategory
on b.B_CategoryID equals bc.BC_CategoryID
select new
{
// put in whatever fields you want returned here:
b.B_BID,
b.B_CategoryID,
b.B_Name,
bi.BI_BID,
bi.BI_IID,
Price = bi.BI_Price,
bc.BC_CategoryID,
CategoryName = bc.BC_CategoryName
};
I have supposed inner joins (your FKs is not null), so i would like query like this:
var ctx = new YourEntities();
var query = from b in ctx.B_Book
from bi in ctx.BI_BookInstance
from bc in ctx.BC_BookCategory
where b.B_BID == bi.BI_BID && b.B_CategoryID == bc.BC_CategoryID
select new
{
BInstID = bi.BI_IID,
BName = b.B_Name,
BPrice = bi.BI_Price,
BCategory = bc.BC_CategoryName
};
foreach (var item in query)
{
Console.WriteLine(item.BInstID);
Console.WriteLine(item.BName);
Console.WriteLine(item.BPrice);
Console.WriteLine(item.BCategory);
Console.WriteLine("");
}
You can do this without explicitly using linq's join statement, provided that navigation properties are in place:
from b in ctx.B_Book
from bi in b.BookInstances
select new { b.Property1, bi.Property2, b.BookCategory.Name }
I have an application that successfully utilizes LINQ to perform LEFT OUTER JOINs several instances; however, in one case it fails to work as expected.
Testing in LINQPad (using LINQ-to_SQL) produced the correct result; however, to be sure I changed to the LINQPad beta version 4.42.05 and successfully connected using my application's DLL and the connectionString from its web.config file (as per the Add Connection dialog). Again, LINQPad is successful in returning the proper result and clearly generates the expected left outer join in TSQL but the same code in the application fails.
In debugging the function, I get the "Object reference not set to an instance of an object." error. Please see additional descriptions after the following code and related TSQL. Note the relationship involves customer who have one-or-more stores and whoes stores have zero-or-more departments. Therefore, some returned records will not have a department (hence the requirement for the left outer join).
The following code works perfectly in LINQPad:
var model = (from h in SalesOrderHeaders
join c in Customers on h.CustomerId equals c.CustomerId
join s in Stores on h.StoreId equals s.StoreId
join d in Departments on h.DepartmentId equals d.DepartmentId into outer
from o in outer.DefaultIfEmpty()
select new
{
OrderId = h.SalesOrderHeaderId,
OrderDetailId = 1,
SalesOrderDate = h.SalesOrderDate,
DeliveryDateTime = h.DeliveryDateTime,
Customer = c.Customer,
Store = s.Store,
Department = (o.Department == null) ? "None" : o.Department,
FullDescription = "None",
Qty = 0,
UoM = "None",
}).OrderBy (m => m.OrderId);
When the code below is used in the application it fails:
var model = from h in headers
join c in customers on h.CustomerId equals c.CustomerId
join s in stores on h.StoreId equals s.StoreId
join d in departments on h.DepartmentId equals d.DepartmentId into outer
from o in outer.DefaultIfEmpty()
select new SalesOrderGridViewModel
{
OrderId = h.SalesOrderHeaderId,
OrderDetailId = 1,
SalesOrderDate = h.SalesOrderDate,
DeliveryDateTime = h.DeliveryDateTime,
Customer = c.Name,
Store = s.Name,
Department = (o.Name == null) ? "None" : o.Name,
FullDescription = "None",
Qty = 0,
UoM = "None",
};
However, when I change the code in the application so that the boolean in the assignment of the department field of the result references the join element from the headers variable (h.DepartmentId == null) as in the following code:
var model = from h in headers
join c in customers on h.CustomerId equals c.CustomerId
join s in stores on h.StoreId equals s.StoreId
join d in departments on h.DepartmentId equals d.DepartmentId into outer
from o in outer.DefaultIfEmpty()
select new SalesOrderGridViewModel
{
OrderId = h.SalesOrderHeaderId,
OrderDetailId = 1,
SalesOrderDate = h.SalesOrderDate,
DeliveryDateTime = h.DeliveryDateTime,
Customer = c.Name,
Store = s.Name,
Department = (h.DepartmentId == null) ? "None" : o.Name,
FullDescription = "None",
Qty = 0,
UoM = "None",
};
The expected result is returned.
Interestingly the subtle difference in the TSQL generated first from the original code:
SELECT [t4].[SalesOrderHeaderId] AS [OrderId], [t4].[SalesOrderDate],
[t4].[DeliveryDateTime], [t4].[Customer], [t4].[Store],
[t4].[value] AS [Department]
FROM (
SELECT [t0].[SalesOrderHeaderId], [t0].[SalesOrderDate],
[t0].[DeliveryDateTime], [t1].[Customer], [t2].[Store],
(CASE
WHEN [t3].[Department] IS NOT NULL THEN [t3].[Department]
ELSE CONVERT(NVarChar(50),#p0)
END) AS [value]
FROM [SalesOrderHeaders] AS [t0]
INNER JOIN [Customers] AS [t1] ON [t0].[CustomerId] = [t1].[CustomerId]
INNER JOIN [Stores] AS [t2] ON [t0].[StoreId] = ([t2].[StoreId])
LEFT OUTER JOIN [Departments] AS [t3]
ON [t0].[DepartmentId] = ([t3].[DepartmentId])) AS [t4]
ORDER BY [t4].[SalesOrderHeaderId]
And here from the revised code, where the boolean was changed to test the value of the DepartmentId in the original headers table ([t3].[Department] versus [t0].[DepartmentId] ), appears to be the solution:
SELECT [t4].[SalesOrderHeaderId] AS [OrderId], [t4].[SalesOrderDate],
[t4].[DeliveryDateTime], [t4].[Customer], [t4].[Store],
[t4].[value] AS [Department]
FROM (
SELECT [t0].[SalesOrderHeaderId], [t0].[SalesOrderDate],
[t0].[DeliveryDateTime], [t1].[Customer], [t2].[Store],
(CASE
WHEN [t0].[DepartmentId] IS NOT NULL THEN [t3].[Department]
ELSE CONVERT(NVarChar(50),#p0)
END) AS [value]
FROM [SalesOrderHeaders] AS [t0]
INNER JOIN [Customers] AS [t1] ON [t0].[CustomerId] = [t1].[CustomerId]
INNER JOIN [Stores] AS [t2] ON [t0].[StoreId] = ([t2].[StoreId])
LEFT OUTER JOIN [Departments] AS [t3]
ON [t0].[DepartmentId] = ([t3].[DepartmentId])) AS [t4]
ORDER BY [t4].[SalesOrderHeaderId]
While I have found a way to make this work; because it works both ways in LINQPad and successfully in numerous other LINQ queries scattered throughout my application, its failure in the original form in this one location gives me concern.
Ultimately, it appears to fail in the application when I test the returned value of the left outer join. However, this is the documented practice in many books and articles. So my final question is does anyone have any insight into why this would occur and/or how it can work in LINQPad (using the applications DLL and against the same DB)?
This is a classic example of how not to write LINQ queries - thinking in SQL and then transliterating into LINQ.
With LINQ, you can avoid the joins completely and formulate your query as follows:
from h in SalesOrderHeaders
orderby h.OrderId
select new
{
OrderId = h.SalesOrderHeaderId,
OrderDetailId = 1,
SalesOrderDate = h.SalesOrderDate,
DeliveryDateTime = h.DeliveryDateTime,
c.Customer.Customer,
s.Store.Store,
Department = (h.Department == null) ? "None" : h.Department.Department,
FullDescription = "None",
Qty = 0,
UoM = "None"
}
It appears that [t0].DepartmentID (from SalesOrderHeaders) can be null. Your LEFT OUTER JOIN relies on this value. This ends up comparing [t3].DepartmentID to null (in some cases).
You might need to use your CASE statement from the select in the JOIN as well.