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Implementation of [PARTITION BY] command by LINQ

I did my best search to convert PARTION BY command from TSQL to LINQ command. But apparently there is no way to convert it.
This is my code to which I am going to convert:
WITH MyRowSet
AS
(
SELECT OrderDate
,SalesOrderNumber
,AccountNumber
,CustomerID
,ROW_NUMBER() OVER (PARTITION BY CustomerID ORDER BY CustomerID, OrderDate DESC) AS RowNum
FROM [Sales].[SalesOrderHeader]
)
SELECT * FROM MyRowSet WHERE RowNum = 1
If exist any solution I would be greatful to know.

linq2db has this feature among with CTE. If you already work with EF Core, you can extend your LINQ queries by extension linq2db.EntityFrameworkCore
This SQL can be written by LINQ
var rnQuery =
from oh in db.SalesOrderHeader
select new
{
oh.OrderDate,
oh.SalesOrderNumber,
oh.AccountNumber,
oh.CustomerID,
RowNum = Sql.Ext.RowNumber().Over().PartitionBy(oh.CustomerID)
.OrderByDesc(oh.OrderDate).ToValue()
};
// switch to alternative LINQ Translator
rnQuery = rnQuery.ToLinqToDB();
var query =
from q in rnQuery.AsCte("MyRowSet")
where q.RowNum == 1
select q;
I have simplified your OrderBy - CustomerID is not needed if you are making partition by this field.

While Selecting based on ROWID - Distinct or Group By doesn't work in oracle

I have query like below , I tried to filter out duplicate columns by using Group BY
SELECT contacts.rowid AS ROW_PASS,
duty_rota.rowid AS ROW_PASS_ROTA,
duty_rota.duty_type AS DUTY_TYPE
FROM duty_rota,
duty_types,
contacts
WHERE duty_rota.duty_type = duty_types.duty_type
AND duty_rota.duty_officer = contacts.duty_id
AND sname IS NOT NULL
GROUP BY contacts.rowid,
duty_rota.rowid,
duty_rota.duty_type
ORDER BY duty_date
After playing with the query little bit I came to know we can't filter out distinct using group by while using ROWID. So can somebody please help me to write code (in SQL) with a logic that
if (any row is completely identical with another row of the query o/p)
{
then display only one column
}
I will be using the output as gridview's data source in C#, so if not in SQL - can you help me whether somehow in C# I can achieve to display only identical columns?

If you want to filter duplicate rows, you can use this query:
SELECT Max(duty_rota.rowid) AS ROW_PASS_ROTA,
duty_rota.duty_type AS DUTY_TYPE
FROM duty_rota,
duty_types,
contacts
WHERE duty_rota.duty_type = duty_types.duty_type
AND duty_rota.duty_officer = contacts.duty_id
AND sname IS NOT NULL
GROUP BY duty_rota.duty_type
ORDER BY DUTY_TYPE

Here you go: http://sqlfiddle.com/#!2/2a038/2
Take out the ROWID's. Example: If your table has 3 columns (colA, colB, colC) you could find exact row dups this way...
select a.* from
(
select count(*) dupCnt, colA, colB, colC from myTable
group by colA, colB, colC
) a
where dupCnt > 1

First, the ROWID is a unique field for each row, so using this field you will never have duplicates. The only solution here is to not use it. It's data does not hold anything you would want to display anyway.
Simply put, if you want no duplicates, you need the DISTINCT keyword:
SELECT DISTINCT field1,
field2
FROM table1,
table2
WHERE table1.key1 = table2.key1;
This will select all Field1, Field2 combinations from the two tables. Due to the DISTINCT keyword, each line will only be in the result list once. Duplicates will not be in the result list.
SELECT DISTINCT duty_rota.duty_type AS DUTY_TYPE
FROM duty_rota,
duty_types,
contacts
WHERE duty_rota.duty_type = duty_types.duty_type
AND duty_rota.duty_officer = contacts.duty_id
AND sname IS NOT NULL
ORDER BY duty_date
You will only need to GROUP BY if you need further operations on the result set, like counting the duplicates. If all you need is "no duplicates", the DISTINCT keyword is exactly what you are looking for.
Edit:
In case I misread your question and you want to see only those, that are duplicates, you need to group and you need to filter based on the groups criteria. You can do that using the HAVING clause. It's kind of an additional WHERE of the groups criteria:
SELECT FIELD1, FIELD2, COUNT(*)
FROM TABLE1, TABLE2
WHERE TABLE1.KEY1 = TABLE2.KEY1
GROUPB BY FIELD1, FIELD2
HAVING COUNT(*) > 1

Get total row count in Entity Framework

I'm using Entity Framework to get the total row count for a table. I simply want the row count, no where clause or anything like that. The following query works, but is slow. It took about 7 seconds to return the count of 4475.
My guess here is that it's iterating through the entire table, just like how IEnumerable.Count() extension method works.
Is there a way I can get the total row count "quickly"? is there a better way?
public int GetLogCount()
{
using (var context = new my_db_entities(connection_string))
{
return context.Logs.Count();
}
}

You can even fire Raw SQL query using entity framework as below:
var sql = "SELECT COUNT(*) FROM dbo.Logs";
var total = context.Database.SqlQuery<int>(sql).Single();

That is the way to get your row count using Entity Framework. You will probably see faster performance on the second+ queries as there is an initialization cost the first time that you run it. (And it should be generating a Select Count() query here, not iterating through each row).
If you are interested in a faster way to get the raw row count in a table, then you might want to try using a mini ORM like Dapper or OrmLite.
You should also make sure that your table is properly defined (at the very least, that it has a Primary Key), as failure to do this can also affect the time to count rows in the table.

If you have access to do so, it would be much quicker to query the sys tables to pull this information.
E.g.
public Int64 GetLogCount()
{
var tableNameParam = new SqlParameter("TableName", "Logs");
var schemaNameParam = new SqlParameter("SchemaName", "dbo");
using (var context = new my_db_entities(connection_string))
{
var query = #"
SELECT ISNULL([RowCount],0)
FROM (
SELECT SchemaName,
TableName,
Sum(I.rowcnt) [RowCount]
FROM sysindexes I
JOIN sysobjects O (nolock) ON I.id = o.id AND o.type = 'U'
JOIN (
SELECT so.object_id,
ss.name as SchemaName,
so.name as TableName
FROM sys.objects SO (nolock)
JOIN sys.schemas SS (nolock) ON ss.schema_id = so.schema_id
) SN
ON SN.object_id = o.id
WHERE I.indid IN ( 0, 1 )
AND TableName = #TableName AND SchemaName = #SchemaName
GROUP BY
SchemaName, TableName
) A
";
return context.ExecuteStoreQuery<Int64>(query, tableNameParam, schemaNameParam).First();
}
}

Linq to SQL | Top 5 Distinct Order by Date

I have an SQL query which I want to call from LINQ to SQL in asp.net application.
SELECT TOP 5 *
FROM (SELECT SongId,
DateInserted,
ROW_NUMBER()
OVER(
PARTITION BY SongId
ORDER BY DateInserted DESC) rn
FROM DownloadHistory) t
WHERE t.rn = 1
ORDER BY DateInserted DESC
I don't know whether its possible or not through linq to sql, if not then please provide any other way around.

I think you'd have to change the SQL partition to a Linq group-by. (Effectively all the partition does is group by song, and select the newest row for each group.) So something like this:
IEnumerable<DownloadHistory> top5Results = DownloadHistory
// group by SongId
.GroupBy(row => row.SongId)
// for each group, select the newest row
.Select(grp =>
grp.OrderByDescending(historyItem => historyItem.DateInserted)
.FirstOrDefault()
)
// get the newest 5 from the results of the newest-1-per-song partition
.OrderByDescending(historyItem => historyItem.DateInserted)
.Take(5);

Although McGarnagle answer solves the problem, but when i see the execution plan for the two queries, it was really amazing to see that linq to sql was really too slow as compare to native sql queries. See the generated query for the above linq to sql:
--It took 99% of the two execution
SELECT TOP (5) [t3].[SongId], [t3].[DateInserted]
FROM (
SELECT [t0].[SongId]
FROM [dbo].[DownloadHistory] AS [t0]
GROUP BY [t0].[SongId]
) AS [t1]
OUTER APPLY (
SELECT TOP (1) [t2].[SongId], [t2].[DateInserted]
FROM [dbo].[DownloadHistory] AS [t2]
WHERE [t1].[SongId] = [t2].[SongId]
ORDER BY [t2].[DateInserted] DESC
) AS [t3]
ORDER BY [t3].[DateInserted] DESC
--It took 1% of the two execution
SELECT TOP 5 t.SongId,t.DateInserted
FROM (SELECT SongId,
DateInserted,
ROW_NUMBER()
OVER(
PARTITION BY SongId
ORDER BY DateInserted DESC) rn
FROM DownloadHistory) t
WHERE t.rn = 1
ORDER BY DateInserted DESC

How to translate SQL statement with multiple join conditions based on subquery to LINQ

This might be one of those situations where plain SQL commands are better than LINQ. Here's a simplified version of the SQL statement I'm trying to translate:
SELECT * FROM IDTable AS idt
INNER JOIN NameTable AS nt ON nt.IDTableID=idt.Id
AND nt.Id= (SELECT TOP(1) Id
FROM NameTable AS nt2
WHERE nt2.IDTableID=11 ORDER BY nt2.DateInserted DESC)
I have the LINQ query to pull records when just joining on IDs and I've seen how to join on multiple columns, but I have no idea how to plug the subquery into the mix.
If this isnt entirely clear, please let me know and I'll edit to elaborate.

Maybe something like this?
var results = from id in db.IDTable
join n in db.NameTable on id.Id equals n.IDTableID
where n.Id = (
from n2 in db.NameTable
where n2.IDTableID = 11
orderby n2.DateInserted desc
).First()
select new { id, n };