I need to execute SQL query with output parameter.
For example,
SELECT #Count = COUNT(*) FROM dbo.SomeTable
SELECT * FROM SomeTable WHERE Id BETWEEN 1 AND 10
After quering I need to know the #Count value.
How can I do it with LINQ without using a stored procedure?
Thank you.
int value = yourDB.SomeTable.Count(q=>q.id >=1 && q.id <= 10);
linq is pretty easy :)
edit: so you want 2 items, the count, and then a limited part of the array.
List<SomeTable> li = yourDB.SomeTable.ToList();
int number = li.Count;
List<SomeTable> partial = li.GetRange(0, 10);
or
int value = yourDB.SomeTable.Count();
List<SomeTable> partial = yourDB.SomeTable.ToList().GetRange(0, 10);
so the best LINQ thing for paging is:
List<SomeTable> partial = yourDB.SomeTable.OrderBy(q=>q.id).Skip(0).Take(10).ToList();
Related
I have a query that selects a single column and I am executing the query in batches using setFirstResults & setMaxResults methods of SQLQuery.
Snippet:
SQLQuery query = <query object with query projecting a single column>;
int maxResults = 50;
int batchSize = 50;
for (int i = 0; ; i++) {
query.setFirstResult(batchSize*i);
query.setMaxResults(maxResults);
List resultSet = query.list();
if(resultSet.isEmpty())
break;
//process result set
}
I set to true the showSQL parameter in hibernate config to see the query string that hibernate produces. For the first batch, i.e. when i=0 below is the query that hibernate generates:
select * from (/* query selecting single column here */) where rownum <= ?;
which makes sense since its the first batch and we want results from first row and rownum is used to restrict the number of results to maxResults.
Now for the second and subsequent batch reads, the query hibernate generates is:
select * from ( select row_.*, rownum rownum_ from (/*query selecting single column here */) row_ where rownum <= ?) where rownum_ > ?;
and you can clearly see, the above query is selecting two columns, one being the row number itself.
So when my query only selects one column, hibernate's version of the query is selecting two.
Is this known issue? Can I do something different or am I doing something wrong?
I don't want to cast the result set into two different types before using/processing it.
i need help with the following dax statement.
Situation:
I have 2 tables. One table contains sell data with articleIDs, dateIDs and sell prices, another table contains stock movements data with articleIDs, dateIDs and purchase prices. According to the dateID i want to write the purchase prices into the first table using a calculated column because i need the prices for every row.
Example:
Table1 t1
t1.articleID = 123; t1.dateID = 20160905; t1.sellPrice = 62,55; t1.purchasePrice = My DAX Statement
Table2 t2
t2.articleID = 123; t2.dateID = 20160905; t2.purchasePrice = 37,07
t2.articleID = 123; t2.dateID = 20160905; t2.purchasePrice = 37,07
t2.articleID = 123; t2.dateID = 20160906; t2.purchasePrice = 37,07
t2.articleID = 456; t2.dateID = 20160905; t2.purchasePrice = 12,15
My DAX Statement:
= CALCULATE (
VALUES (t2[purchasePrice]);
TOPN (
1;
FILTER(FILTER(t2; t2[articleID] = t1[articleID]); t2[dateID] <= t1[dateID]); t2[dateID]; DESC
)
)
With my DAX Statement i get the following error:
A table of multiple values was supplied where a single value was expected.
It is normal that i have more than one row matching in the table 2.
Actually I just want the price of any of them on the corresponding dateID, even if they are tied. So i used the TOPN function with the value 1 and sorted by date but the error still remains. Is there a way to fix my DAX Statement to achieve this?
Create a calculated column in T1 and use this expression:
purchasePrice =
CALCULATE (
MAX ( T2[purchasePrice] ),
FILTER ( T2, T1[ArticleID] = T2[articleID] && T1[DateID] = T2[dateID] )
)
Note I use comma to separate passed arguments to the functions but I see in your expression you used semicolon. Change it to match your system list separator.
It is not tested but should work. Let me know if it works for you.
I want to calculate a Sum value using fields from 2 tables and can't work out the syntax.
var x = (from l in context.Lessons
join t in context.Tariffs on l.TariffId equals t.Id
where l.StudentSemesterId == studentSemesterId
select new {
lessonCost = (t.Rate) * (l.Duration / 60)
});
This returns a set of values for individual lessons. How do I get the Sum total of these lessons?
You are selecting a new IEnumerable of an anonymous object type. Just select the correct value you are looking for. Then you have IEnumerable of float/double/decimal/whatever. Then take the resulting sum of that query.
var x = (from l in context.Lessons
join t in context.Tariffs on l.TariffId equals t.Id
where l.StudentSemesterId == studentSemesterId
select (t.Rate) * (l.Duration /60)).Sum();
my table consists of 3 columns(sno,name,age) now i am retrieving this table from the database with extra column(row number) ,i used the following code
select * from (
select ROW_NUMBER() over (order by SNo asc)as rowindex,SNo,Name,Age
from tblExample)
as example where rowindex between ((pageindex*10)+1) and ((pageindex+1)*10)
note:here pageindex is the varaible that takes some intger value which is passed by the user
my data base is sql server 2008, now i want to write the same query using linq
can any one please change the abovesql query into linq. iam unable to do it as iam new to linq. iam struck up with this problem please help me thank you in advance
You can write query as beow
var index=1;
var pageIndex=1;
var pageSize = 10;
data.Select(x => new
{
RowIndex = index++,
Sno = x.Sno,
Name = x.Name,
Age = x.Age
}).OrderBy(x => x.Name)
.Skip(pageSize * (pageIndex - 1)).Take(pageSize).ToList();
I have a query that looks like this:
public IList<Post> FetchLatestOrders(int pageIndex, int recordCount)
{
DatabaseDataContext db = new DatabaseDataContext();
return (from o in db.Orders
orderby o.CreatedDate descending
select o)
.Skip(pageIndex * recordCount)
.Take(recordCount)
.ToList();
}
I need to print the information of the order and the user who created it:
foreach (var o in FetchLatestOrders(0, 10))
{
Console.WriteLine("{0} {1}", o.Code, o.Customer.Name);
}
This produces a SQL query to bring the orders and one query for each order to bring the customer. Is it possible to optimize the query so that it brings the orders and it's customer in one SQL query?
Thanks
UDPATE: By suggestion of sirrocco I changed the query like this and it works. Only one select query is generated:
public IList<Post> FetchLatestOrders(int pageIndex, int recordCount)
{
var options = new DataLoadOptions();
options.LoadWith<Post>(o => o.Customer);
using (var db = new DatabaseDataContext())
{
db.LoadOptions = options;
return (from o in db.Orders
orderby o.CreatedDate descending
select o)
.Skip(pageIndex * recordCount)
.Take(recordCount)
.ToList();
}
}
Thanks sirrocco.
Something else you can do is EagerLoading. In Linq2SQL you can use LoadOptions : More on LoadOptions
One VERY weird thing about L2S is that you can set LoadOptions only before the first query is sent to the Database.
you might want to look into using compiled queries
have a look at http://www.3devs.com/?p=3
Given a LINQ statement like:
context.Cars
.OrderBy(x => x.Id)
.Skip(50000)
.Take(1000)
.ToList();
This roughly gets translated into:
select * from [Cars] order by [Cars].[Id] asc offset 50000 rows fetch next 1000 rows
Because offset and fetch are extensions of order by, they are not executed until after the select-portion runs (google). This means an expensive select with lots of join-statements are executed on the whole dataset ([Cars]) prior to getting the fetched-results.
Optimize the statement
All that is needed is taking the OrderBy, Skip, and Take statements and putting them into a Where-clause:
context.Cars
.Where(x => context.Cars.OrderBy(y => y.Id).Select(y => y.Id).Skip(50000).Take(1000).Contains(x.Id))
.ToList();
This roughly gets translated into:
exec sp_executesql N'
select * from [Cars]
where exists
(select 1 from
(select [Cars].[Id] from [Cars] order by [Cars].[Id] asc offset #p__linq__0 rows fetch next #p__linq__1 rows only
) as [Limit1]
where [Limit1].[Id] = [Cars].[Id]
)
order by [Cars].[Id] asc',N'#p__linq__0 int,#p__linq__1 int',#p__linq__0=50000,#p__linq__1=1000
So now, the outer select-statement only executes on the filtered dataset based on the where exists-clause!
Again, your mileage may vary on how much query time is saved by making the change. General rule of thumb is the more complex your select-statement and the deeper into the dataset you want to go, the more this optimization will help.