I have a sql table called expenses with an int column called cost. In my application this data is displayed on a grid which is refreshing every time I insert a new row with a linq2sql insert. What I would like to do is have an integer variable in my application that is the sum of all the fields in the cost column every time I insert a row.
Is there a simple way to sum these fields with linq2sql every time I do an insert. Please try to avoid lambda as I haven't gotten to learning that yet.
Thanks!
Assuming that you use query syntax instead of lambdas, here you are:
var totalCost = (from expensesRow in dataContext.Expenses
select expensesRow.cost)
.Sum();
Which in fact is the same as:
var totalCost = dataContext.Expenses
.Sum(x => x.cost);
Here dataContext is an instance of your Linq2Sql DataContext class.
You get to learn lambdas today. http://www.theabsentmindedcoder.com/2010/06/linq-sum.html has exactly what you want, and uses a very simple lambda to get there. You could get away without the lambda by making your select gather up only the one column of integers you're trying to sum, but why do extra work to not learn things?
Say I had a table called users with the following structure:
[Table users] - id | username | points_awarded
Then, I can find the total number of points I awarded every user by running the query:
SELECT SUM(points_awarded) as total_points FROM users
You can also count how many users have points greater than our equal to N. For example, says N = 500, then I can run:
SELECT COUNT(id) as num_users_with_points FROM users WHERE points_award >= 500
Check out:
http://dev.mysql.com/doc/refman/5.1/en/counting-rows.html
http://dev.mysql.com/doc/refman/5.0/en/func-op-summary-ref.html
for more information.
Related
I have multiple random numbers in table column ID like
8v12027
8v12025
8v12024
8v12029.
8v12023
8v12030
8v12020
O/p - 8v12020, From 8v12023 To 8v12025, 8v12027, From 8v12029 To 8v12030,
I assume you'are waiting for an sql solution so :
You have to use Lead or Lag KeyWord and concat it.
SELECT CONCAT('From ',Id,'To :', LEAD(p.Id) OVER (ORDER BY p.Id),'s') FROM YourTable p
There is a really good explanation about thoses keyword in the sqlauthority web site.
https://blog.sqlauthority.com/2013/09/22/sql-server-how-to-access-the-previous-row-and-next-row-value-in-select-statement/
But If you were waiting for a pure C# solution, you can retreive the data set in an Array, after order it by Id and concat and with a for loop concat current value with previous (or next) one.
Or with a Linq use Aggregate
yourArray.Aggregate((a,b)=> String.Concat("From ",a," To ",b,";")).Split(';')
I have List of object like this
List<Product> _products;
Then I get productId input and search in this list like this
var target = _peoducts.Where(o => o.productid == input).FirstOrDefault();
my Question is
If This list have 100 Products (productId from 1 to 100) and an
input I get productId = 100. that mean this Method must loop for 100
time Right ? (If I ORDER BY productId ASC in Query)
Between use this Method and Query on Database with where clause like
this WHERE productId = #param
Thank you.
No. If there is an index with key productId it finds the correct row with O(log n) operations
Just implement both methods and take the time. (hint: use StopWatch() class)
Edit
To get the full performance you should not create an intermediate (unsorted) List<T> but put all your logic in a LINQ query which operates on the SQL Server.
#might be helpful to get your answer.
https://www.linqpad.net/WhyLINQBeatsSQL.aspx
If you execute that Where on a List<Product>, then:
you got all 100 rows from the database
and then looped through all products in memory until you found the one that matches or until you went through the entire list and found nothing.
If, on the other hand, you used an IQueryable<Product> that was connected to the database table, then:
You wouldn't have read anything from the database yet
When you apply the Where, you still wouldn't read anything
When you apply the FirstOrDefault a sql query is constructed to find just the one row you need. Given correct indexes on the table, this would be quite fast.
I'm using Linq/EF4.1 to pull some results from a database and would like to limit the results to the (X) most recent results. Where X is a number set by the user.
Is there a way to do this?
I'm currently passing them back as a List if this will help with limiting the result set. While I can limit this by looping until I hit X I'd just assume not pass the extra data around.
Just in case it is relevant...
C# MVC3 project running from a SQL Server database.
Use the Take function
int numberOfrecords=10; // read from user
listOfItems.OrderByDescending(x => x.CreatedDate).Take(numberOfrecords)
Assuming listOfItems is List of your entity objects and CreatedDate is a field which has the date created value (used here to do the Order by descending to get recent items).
Take() Function returns a specified number of contiguous elements from the start of a
sequence.
http://msdn.microsoft.com/en-us/library/bb503062.aspx
results = results.OrderByDescending(x=>x.Date).Take(10);
The OrderByDescending(...) will sort items by your date/time property (or w/e logic you want to use to get most recent) and Take(...) will limit to first x items (first being most recent, thanks to the ordering).
Edit: To return some rows not starting at the first row, use Skip():
results = results.OrderByDescending(x=>x.Date).Skip(50).Take(10);
Use Take(), before converting to a List. This way EF can optimize the query it creates and only return the data you need.
I'm trying to use paging in conjunction with a sum projection to get a sum of the values in a column for just the page of results I'm interested in. I'm using .NET, C# and NHibernate 3.1
I have an ICriteria to start with which is related to all rows from the associated db table.
I'm then doing the following to get a version with the first page (say, 10 items out of 40):
ICriteria recordsCriteria = CriteriaTransformer.Clone(criteria);
recordsCriteria.SetFirstResult(0);
recordsCriteria.SetMaxResults(10);
I'm using this ICriteria for something else so I then create two further clones:
ICriteria totalAggCriteria = CriteriaTransformer.Clone(criteria);
ICriteria pageAggCriteria = CriteriaTransformer.Clone(recordsCriteria);
If I take a look inside these two new ones the first has 40 items in and the second has 10 - exactly what I want.
Let's say the objects coming back from the DB have a column called "ColA" and it's of type Int32.
From this, I want the sum of all 40 ColA values and the sum of the first 10 ColA values.
To get the sum of all 40 ColA values, I do the following:
totalAggCriteria.SetProjection(NHibernate.Criterion.Projections.Sum("ColA"));
var totalSum = totalAggCriteria.UniqueResult();
The value in totalSum is correct.
To get the sum of the first 10 ColA values, I'm trying the following:
pageAggCriteria.SetProjection(NHibernate.Criterion.Projections.Sum("ColA"));
vat pageSum = pageAddCriteria.UniqueResult();
However, this gives me the same value as the previous one - for all 40 ColA values.
I've also tried the following but it gives the same result:
pageAggCriteria.SetProjection(NHibernate.Criterion.Projections.Sum(column));
pageAggCriteria.SetFirstResult(firstResult.Value);
pageAggCriteria.SetMaxResults(pageSize.Value);
pageSum = pageAggCriteria.UniqueResult();
And also:
pageAggCriteria.SetFirstResult(firstResult.Value);
pageAggCriteria.SetMaxResults(pageSize.Value);
pageAggCriteria.SetProjection(NHibernate.Criterion.Projections.Sum(column));
pageSum = pageAggCriteria.UniqueResult();
Can anyone give an idea on where I'm going wrong and how I can actually get the sum of the ColA values in the first 10 results?
Thanks
Probably easiest to do that sum client side. The aggregate function is operating on the whole table. What you are trying to do is run the aggregate function against the paged result which I don't think is possible with NH.
In other words, you want select sum(colA) from (select top 10 ...) but that criteria will give you select top 10 sum(colA) from ...)
Is it possible to return a single value and an enumerable collection using LINQ to SQL?
The problem is, I'm trying to do paging across a large recordset. I only want to return 10 rows at a time so I'm using .Skip(20).Take(10) approach.
However I need to know the total number of records so I can show an appropriate page x of y.
Trying to avoid two separate queries.
Thanks
Don't be afraid of queries. Do both.
I came across this exact same issue and ended up with
var q = from i in tableName select i;
int total = q.Count();
foreach(var obj in q.Skip(20).Take(10))
{
...
}
It really wasn't a problem at all