Magic tables are the logical temporary tables created by the SQL server internally to recover recently inserted, deleted, and updated data into the SQL server. They are created during DML trigger execution. If you want to know more about DML triggers, you may refer to my previous article on DML Triggers.

Three types of Magic tables are created at the time of insert/update/delete in the SQL server.
    INSERTED Magic tables
    DELETED Magic tables
    UPDATED Magic tables

Magic tables are stored in temp DB just as a temporary internal table, and we can see them with the help of triggers. We can retrieve the information or the impacted records using these Magic tables.

Let’s see how this works with the use of a trigger.
    When we perform the insert operation, the inserted magic table will have a recently inserted record showing on top of the table.
    When we perform the delete operation, the deleted magic table will have a recently deleted record showing on top of the table.
    When we perform the update operation, the inserted magic table will have a recently updated record showing on top of the table.

Let’s consider the below table to see how this work.
SELECT * FROM StudentsReport;

Inserted Magic Table
Let’s create a trigger on the StudentsReport table to see if the values are inserted on the StudentsReport table and see if a virtual table or temp table (Magic table) is created with recently inserted records.

CREATE TRIGGER  TR_StudentsReport_InsertedMagic ON StudentsReport
FOR INSERT
AS
BEGIN
    SELECT * FROM INSERTED
END

Now when we insert the records in the StudentsReport table, at the same time inserted magic table will be created along with recently inserted records.

Now execute the below queries together.
INSERT INTO StudentsReport VALUES (6, 'Peter', 'English', 90);
SELECT * FROM StudentsReport;

We can see that while inserting a record in the StudentsReport table, it’s showing a recently Inserted record in the temp table, and that temp table is inserted magic table.
Deleted Magic Table

Now let’s create a trigger on the StudentsReport table to see if the values are deleted from the StudentsReport table and if the Magic table is created for recently deleted records.

CREATE TRIGGER  TR_StudentsReport_DeletedMagic ON StudentsReport
FOR DELETE
AS
BEGIN
    SELECT * FROM Deleted
END

we can see that while deleting a record from the StudentsReport table, it’s also showing a recently deleted record in the temp table, and that temp table is deleted magic table.

Updated Magic Table

Now, Let’s create a trigger on the StudentsReport table to see if the values are updated on the StudentsReport table and if the Magic table is created for recently updated records.
CREATE TRIGGER  TR_StudentsReport_UpdatedMagic ON StudentsReport
FOR UPDATE
AS
BEGIN
    SELECT * FROM INSERTED
END

Now when we update the records in the StudentsReport table, at the same time updated magic table will be created along with recently updated records.
Now execute the below query together.
UPDATE StudentsReport SET Marks = 90 WHERE StudentId = 3;
SELECT * FROM StudentsReport;

we can see that while updating the record in the StudentsReport table, it’s also showing a recently updated record in the temp table, and that temp table is an updated magic table.

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In this article, we will learn about SPARSE Column in SQL Server. The SPARSE column is a good feature of SQL Server. It helps us to reduce the space requirements for null values. Using a SPARSE column, we may save up to 20 to 40 percent of space.

SPARSE Column in SQL ServerA SPARSE column is a common column with optimized storage for NULL values. It also reduces the space requirements for null values at the cost of more overhead to retrieve non-null values. In other words, a SPARSE column is better at managing NULL and ZERO values in SQL Server. It does not occupy any space in the database. Using a SPARSE column, we may save up to 20 to 40 percent of the area. We can define a column as a SPARSE column using the CREATE TABLE or ALTER TABLE statements.
CREATE TABLE TableName
(
      .....
      Col1 INT SPARSE,
      Col2 VARCHAR(100) SPARSE,
      Col3 DateTime SPARSE
      .....
)

We may also add/change a column from the graphical view.

Example
In this example, I have created two tables with the same number of columns and the same data type, but one table's columns are created as a SPARSE column. Each table contains 500+ rows.
CREATE TABLE TableName
(
      Col1 INT SPARSE,
      Col2 VARCHAR(100) SPARSE,
      Col3 DateTime SPARSE
)

CREATE TABLE TableName1
(
      Col1 INT ,
      Col2 VARCHAR(100) ,
      Col3 DateTime
)

Using the sp_spaceused stored procedure, we can determine the space occupied by the table data.
sp_spaceused 'TableName'
GO
sp_spaceused 'TableName1'

Advantages of a SPARSE column
    A SPARSE column saves database space when there are zero or null values.
    INSERT, UPDATE, and DELETE statements can reference the SPARSE columns by name.
    We can get more benefits from Filtered indexes on a SPARSE column.
    We can use SPARSE columns with change tracking and change data capture.

Limitations of a SPARSE column
    A SPARSE column must be nullable and cannot have the ROWGUIDCOL or IDENTITY properties.
    A SPARSE column cannot be data types like text, ntext, image, timestamp, user-defined data type, geometry, or geography.
    It cannot have a default value and bounded-to rule.
    A SPARSE column cannot be part of a clustered index or a unique primary key index and partition key of a clustered index or heap.
    Merge replication does not support SPARSE columns.
    The SPARSE property of a column is not preserved when the table is copied.

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Occasionally, we must resize or realign our Tempdb log file (.ldf) or data files (.mdf or .ndf) due to a growth event that forces the file size out of whack. To resize we have three options, restart the SQL Server Service, add additional files, or shrink the current file. We most likely have all been faced with runaway log files and in an emergency situation restarting the SQL Services may not be an option but we still need to get our log file size smaller before we run out of disk space for example. The process of shrinking down that file can get tricky so I created this flow chart to help you out if you ever get into this situation.
 
Now its very important to note that many of these commands will clear your cache and will greatly impact your server performance as it warms cache backup. In addition, you should not shrink your database data or log file unless absolutely necessary. But doing so, it can result in a corrupt tempdb.
 
Let’s walk through it and explain somethings as we go along.
First thing you must do is issue a Checkpoint. A checkpoint marks the log as a “good up to here” point of reference. It lets the SQL Server Database Engine know it can start applying changes contained in the log during recovery after this point if an unexpected shutdown or crash occurs. Anything prior to the check point is what I like to call “Hardened”. This means all the dirty pages in memory have been written to disk, specifically to the .mdf and .ndf files. So, it is important to make that mark in the log before you proceed. Now, we know tempdb is not recovered during a restart it is recreated, however this is still a requirement.
    USE TEMPDB;    
    GO    
    CHECKPOINT;  

Next, we try to shrink the log by issuing a DBCC SHRINKFILE command. This is the step that frees the unallocated space from the database file if there is any unallocated space available. You will note the Shrink? decision block in the diagram after this step. It is possible that there is no unallocated space and you will need to move further along the path to free some up and try again.
    USE TEMPDB;    
    GO   
    DBCC SHRINKFILE (templog, 1000);   --Shrinks it to 1GB  

If the database shrinks, great congratulations, however for some of us we still might have work to do. Next up is to try and free up some of that allocated space by running DBCC DROPCLEANBUFFERS and DBCC FREEPROCCACHE.
DBCC DROPCLEANBUFFERS
 
Clears the clean buffers from the buffer pool and columnstore object pool. This will flush cached indexes and data pages.
    DBCC DROPCLEANBUFFERS WITH NO_INFOMSGS;  

DBCC FREEPROCCACHE
Clears the procedure cache, you are probably familiar with as a performance tuning tool in development. It will clean out all your execution plans from cache which may free up some space in tempdb. As we know though, this will create a performance as your execution plans now have to make it back into cache on their next execution and will not get the benefit of plan reuse. Now it’s not really clear why this works, so I asked tempdb expert Pam Lahoud (B|T) for clarification as to why this has anything to do with tempdb. Both of us are diving into this to understand exactly why this works. I believe it to be related to Tempdb using cached objects and memory objects associated with stored procedures which can have latches and locks on them that need to be release by running this. Check back for further clarification, I'll be updating this as I find out more.
    DBCC FREEPROCCACHE WITH NO_INFOMSGS;  

Once these two commands have been run and you have attempted to free up some space you can now try the DBCC SHRINKFILE command again. For most this should make the shrink possible and you will be good to go. Unfortunately, a few more of us may have to take a couple more steps through to get to that point.
 
The last two things I do when I have no other choice to get my log file smaller is to run those last two commands in the process. These should do the trick and get the log to shrink.
 
DBCC FREESESSIONCACHE
This command will flush any distributed query connection cache, meaning queries that are between two or more servers.
    DBCC FREESESSIONCACHE WITH NO_INFOMSGS;  

DBCC FREESYSTEMCACHE
This command will release all unused remaining cache entries from all cache stores including temp table cache. This covers any temp table or table variables remaining in cache that need to be released.
    DBCC FREESYSTEMCACHE ('ALL');  

In my early days as a database administrator I would have loved to have this diagram. Having some quick steps during stressful situations such as tempdb’s log file filling up on me would have been a huge help. So hopefully someone will find this handy and will be able to use it to take away a little of their stress.

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This article shows how we can determine the size of an entire database using C# and the size of each and every table in the database using a single SQL command. To explain this, it is divided into three sections,

• Getting Size of one Table in the Database using single SQL Command
• Getting Size of each Table in the Database using single SQL Command
• Getting Size of the entire Database using C#

Getting Size of one Table in the Database using single SQL Command
To get the table size in SQL Server, we need to use the system stored procedure sp_spaceused. If we Table Name as an argument, it gives the disk space used by the table and some other information like: Number of rows existing in the table, Total amount of reserved space for Table, Total amount of space reserved for the table but not yet used and Total amount of space used by indexes in Table.

Example
For the ADDRESS table in our database, if we run,
sp_spaceused 'TADDRS'

It will give the following result,

Getting Size of each Table in the Database using single SQL Command

We have seen how we can determine the size of one table. Now, suppose we want to determine the size of each table in the entire database. We could find the size of any table using this command just by changing the Table name in the parameter. Is that right? But would it not be much better if we have a one-line SQL command that gives the size of each table? Right?
 
Fortunately, SQL Server provides a way to do this. A stored procedure "sp_MSforeachtable" could do easily for us!
 
The sp_MSforeachtable stored procedure is one of many undocumented stored procedures tucked away in the depths of SQL Server. You can find more details of "sp_MSforeachtable" in this link.
 
sp_MSforeachtable is an undocumented stored procedure that is not listed in MSDN Books Online and can be used to run a query against each table in the database. In short, you can use this as,
EXEC sp_MSforeachtable @command1="command to run"
 
In the "command to run" put a "?" , where you want the table name to be inserted. For example, to run the sp_spaceused stored procedure for each table in the database, we'd use,

It will give the size of each table (including other details) like,

Getting the Size of the entire Database
Now we want to get the total size used by a database i.e. the additional space used by each table in the database. We have seen in the previous section how we can get the size of each table in the database. Here is sample code in C# that can be used to calculate the size of the entire database.
 
In this, we are executing the same command what we discussed in the above section and are querying the database using simple ADO.Net. We get the result in a DataSet and then iterate each table to get its size. The table size is stored in the "data" column of each table (see the above Picture-1). We just add the "data" column value of each table to get the size of the entire database. Sample code is also attached with this article.
    class MemorySizeCalculator  
    {  
      public void GetDbSize()  
      {  
        int sum = 0;  
       
     // Database Connection String   
     string sConnectionString = "Server = .; Integrated Security = true; database = HKS";  
       
      // SQL Command [Same command discussed in section-B of this article]  
      string sSqlquery = "EXEC sp_MSforeachtable @command1=\"EXEC sp_spaceused '?'\" ";  
       
      DataSet oDataSet = new DataSet();  
       
      // Executing SQL Command using ADO.Net  
      using (SqlConnection oConn = new SqlConnection(sConnectionString))  
      {  
             oConn.Open();  
             using (SqlCommand oCmdGetData = new SqlCommand(sSqlquery, oConn))  
             {  
                  oCmdGetData.ExecuteNonQuery();  
                  SqlDataAdapter executeAdapter = new SqlDataAdapter(oCmdGetData);  
                  executeAdapter.Fill(oDataSet);  
             }  
             oConn.Close();  
      }  
      // Iterating each table  
      for (int i = 0; i < oDataSet.Tables.Count; i++)  
      {  
        // We want to add only "data" column value of each table  
        sum = sum + Convert.ToInt32(oDataSet.Tables[i].Rows[0]["data"].ToString().Replace    
        ("KB", "").Trim());  
      }  
        Console.WriteLine("Total size of the database is : " + sum + " KB");  
     }  
    } 

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I have not found any direct way to call. So, we need to write our own logic inside a method provided by SignalR Library.
 

There is a Hub class provided by the SignalR library.
 
In this class, we have 2 methods.
    OnConnectedAsync()
    OnDisconnectedAsync(Exception exception)

So, the OnConnectedAsync() method will add user and OnDisconnectedAsyn will disconnect a user because when any client gets connected, this OnConnectedAsync method gets called.

In the same way, when any client gets disconnected, then the OnDisconnectedAsync method is called.
 
So, let us see it by example.
 
Step 1
Here, I am going to define a class SignalRHub and inherit the Hub class that provides virtual method and add the Context.ConnectionId: It is a unique id generated by the SignalR HubCallerContext class.
    public class SignalRHub : Hub  
    {  
    public override Task OnConnected()  
    {  
    ConnectedUser.Ids.Add(Context.ConnectionId);  
    return base.OnConnected();  
    }  
    public override Task OnDisconnected()  
    {  
    ConnectedUser.Ids.Remove(Context.ConnectionId);  
    return base.OnDisconnected();  
    }  
    }  

Step 2
In this step, we need to define our class ConnectedUser with property Id that is used to Add/Remove when any client gets connected or disconnected.
 
Let us see this with an example.
    public static class ConnectedUser  
    {  
    public static List<string> Ids = new List<string>();  
    }  

Now, you will get the result of currently connected client using ConnectedUser.Ids.Count.
 
As you see, here I am using a static class that will work fine when you have only one server, but when you will work on multiple servers, then it will not work as expected. In this case, you could use a cache server like Redis cache, SQL cache.

Today, I'm gonna show you how to sort numbers in SQL Server. It's not a difficult task but not an easy way. In the front end are many functions that for sorting values but SQL Server has no predefined function available.

For example I will sort the numbers 12,5,8,64,548,987,6542,4,285,11,26. SQL Server has no array list or array so how can we hold the values after sorting the numbers? SQL Server has temporary tables. Temporary automatically creates and drops the table after the execution.

First of all, create a temporary table. Suppose a problem occurs in SQL Server or during program execution. A Temporary table can't be deleted or dropped the proper way. When we want to create a table a second time a confirm error occurs as in the following:

There is already an object named '#temp' in the database.

So this type of problem is avoided by checking first if the table exists like this:

    IF  EXISTS (SELECT * FROM sys.tables 
    WHERE name = N'#temp' AND type = 'U') --check the #temp already exists in database or not  
    --Not:-  type U stand for user 
    begin 
    drop table #temp 
    end 

If the table already exists in the database then drop the table #temp.

My values are 12,5,8,64,548,987,6542,4,285,11,26. They need to be be split up before the sort. How can we split the numbers? Of course we can at the comma (,).  If I split the at the comma then I get the numbers like this: 12 5 8 64 548 and so on. One question then arises is, how to split the value? Don't worry, I have done that.

select left('12,45,18,95',

CHARINDEX(',','12,45,18,95')-1))

If i run this query it should be return the value is 12

After that everything is fine, we get the value from the #temp table.

    select ROW_NUMBER() over (order by value) 'srNo', value from #temp order by value

The following is a complete Stored Procedure to sort the numbers. 

   ALTER proc [dbo].[Porc_sortnumber] 
    as 
    begin 
    DECLARE @value VARCHAR(MAX)='1,2,5,6,12,88,47,95,56,20' 
    declare @lenth int =1 
    IF  EXISTS (SELECT * FROM sys.tables 
    WHERE name = N'#temp' AND type = 'U') --check the #temp allready exists in database or not  
    --Not:-  type U stand for user 
    begin 
    drop table #temp 
    end 
    create table #temp (id int identity(1,1),value int)  
    while(@lenth!=0 ) 
    begin 
    insert into #temp(value) values(left(@value,(CHARINDEX(',',@value)-1))) 
    set @value= right(@value,len(@value)-((CHARINDEX(',',@value)))) 
    set @lenth=CHARINDEX(',',@value) 
     
    end 
    insert into #temp(value) values(@value) 
    select ROW_NUMBER() over (order by value) 'srNo', value from #temp order by value 
    end 

Output

I hope this article will helpful!

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You have a set of data, and you want to execute a set of queries on the records in a SQL table which are matching with this set of data. You have got a list of Product IDs from the QA department, you need to get the details of those products from the SQL table. And this situation happens frequently. How would you do this? What are the options you have?

Easy solution – You would write select query and put product ID in where clause and get the details. Do this for all the product IDs you have got. Its a time consuming task.
Is there any better way of achieving it where we can get the result in one query?
 
Solution
Yes, we can write a stored procedure, or you can just prepare a set of queries together to run for a single time also.
 
We will use temporary table variable to create arrays in SQL. We will insert the set of data (what you already have) into a temporary array variable. Use While clause, insert into clauses to generate our result table – which will show details of products matching product IDs.
 
Below is a sample set of queries which generates array variable named MYARRAY, you can store your data in this array. Then we will iterate through these array values using WHILE clause, we have used two variables to loop through array – INDEXVAR and TOTALCOUNT. As usual the loop will continue until INDEXVAR is smaller than TOTALCOUNT.
 
Using INDEXVAR and Where clause we will get current array index value. We will use this value to fetch data from actual table and insert it into our temporary result table PRODUCTDETAILSTABLE.
    Use DATABASENAME  
    GO  
      
    DECLARE @PRODUCTDETAILSTABLE table (PRODUCTNAME nvarchar(100), PRODUCTID int, PRODUCTCOST int)  
      
    -- Declare your array table variable  
    DECLARE @MYARRAY table (TEMPCOL nvarchar(50), ARRAYINDEX int identity(1,1) )  
      
    -- Add values to your array table, these are the values which you need to look for in your database  
    INSERT INTO @MYARRAY (TEMPCOL)  
       VALUES  
    ('PRD-2222'), ('PRD-3333'), ('PRD-4563'), ('PRD-4569'), ('PRD-6657'), ('PRD-3452'), ('PRD-6578')  
      
    --select * from @MYARRAY  
      
    DECLARE @INDEXVAR int  
    DECLARE @TOTALCOUNT int  
    DECLARE @CURINDEXEDPRODUCTID nvarchar (50)  
    SET @INDEXVAR = 0  
    SELECT @TOTALCOUNT= COUNT(*) FROM @MYARRAY  
    WHILE @INDEXVAR < @TOTALCOUNT  
    BEGIN  
        SELECT @INDEXVAR = @INDEXVAR + 1  
      
        -- Get value of current indexed product ID from array table  
        SELECT @CURINDEXEDPRODUCTID = TEMPCOL from @MYARRAY where ARRAYINDEX = @INDEXVAR  
      
        -- Get details of Product matching current indexed product ID from array  
        BEGIN  
            INSERT INTO @PRODUCTDETAILSTABLE (PRODUCTNAME, PRODUCTID, PRODUCTCOST)  
            (  
                select top 1 ProductName as PRODUCTNAME, ProductID as PRODUCTID, Cost as PRODUCTCOST  
                FROM  
                dbo.ProductDetails t  
                where t.ProductID= @CURINDEXEDPRODUCTID  
            )   
        END  
    END  
      
    Select * from @PRODUCTDETAILSTABLE  

You might come across a scenario where you need to update a set of records from your database or delete specific rows from your table – at that time you might need these array queries to fulfill your requirements. That’s it for this article. When someone asks you to pull data for specific list of IDs then I hope these queries help you to pull out data easily from the database.

This article will discuss alternative methods for performing cascading deletes using LINQ to SQL.  Cascading delete refers to the action of removing records associated by a foreign key relationship to a record that is the target of a deletion action.  LINQ to SQL does not specifically handle cascading deletes and it is up to the developer to determine whether or not that action is desired.  It is also up to the developer to determine how to go about accomplishing the cascading delete.
 
Problem
The problem with performing a cascading delete is not new to LINQ to SQL and one has essentially the same alternatives for performing such a delete.  The issue is one of determining how to handle the deletion or retention of records associated with a record targeted for deletion where that record maintains a foreign key relationship with records contained within other tables within the database and more specifically where the foreign key fields are not nullable.
 
As an example, consider the customer table within the Northwind database.  The customer table has a foreign key relationship established with the Orders table (which in turn maintains a foreign key relationship with the Order_Details table).  In order to delete a customer which has associated Orders, one needs to dispose of or otherwise handle the associated records in both the Orders and Order_Details tables.  In the LINQ to SQL jargon, the associated tables are referred to as entity sets.
 
LINQ to SQL will not violate the foreign key relationships and if an application attempts to delete a record with such relationships in place, the executing code will throw an exception.
 
Using the Northwind example, if one were to attempt to delete a customer with associated orders, an exception will occur.  That is not really a problem, that is how it should be, otherwise, why have foreign key relationships at all.  The issue is really one of determining if you would really want to delete records with associated entity sets, and if you do, how would you want to handle it - do you want to keep the associated records or delete them right along with the targeted record?

There are several possible alternatives at your disposal.  You can handle the cascading deletes using LINQ to SQL from within your code, or you can handle the foreign key relationships from within SQL Server.
 
If you were to execute this code against the Northwind database, it would create a customer with an associated order and order details.
    try  
    {  
              Customer c = new Customer();  
              c.CustomerID = "AAAAA";  
              c.Address = "554 Westwind Avenue";  
              c.City = "Wichita";  
              c.CompanyName = "HostForLIFE.eu";  
              c.ContactName = "Peter";  
              c.ContactTitle = "Boss";  
              c.Country = "USA";  
              c.Fax = "888-335-5933";  
              c.Phone = "888-225-4934";  
              c.PostalCode = "88888";  
              c.Region = "EA";  
       
              Order_Detail od = new Order_Detail();  
              od.Discount = .25f;  
              od.ProductID = 1;  
              od.Quantity = 25;  
              od.UnitPrice = 25.00M;  
       
              Order o = new Order();  
              o.Order_Details.Add(od);  
              o.Freight = 25.50M;  
              o.EmployeeID = 1;  
              o.CustomerID = "AAAAA";  
       
              c.Orders.Add(o);  
       
              using (NWindDataContext dc = new NWindDataContext())  
              {  
                       var table = dc.GetTable<Customer>();  
                       table.InsertOnSubmit(c);  
                       dc.SubmitChanges();  
              }  
    }  
    catch (Exception ex)  
    {  
              MessageBox.Show(ex.Message);  
    }

But if you then tried to delete the customer without handling the entity sets using something like this:
    using (NWindDataContext dc = new NWindDataContext())  
    {  
       
              var q =  
                       (from c in dc.GetTable<Customer>()  
                       where c.CustomerID == "AAAAA"  
                       select c).Single<Customer>();  
       
                       dc.GetTable<Customer>().DeleteOnSubmit(q);  
                       dc.SubmitChanges();  
    }

Handling the Delete with LINQ to SQL
You can handle the cascading deletes manually deleting all of the related entities in the associated entity set; here is a simple approach to doing that:
    try  
    {  
              using (NWindDataContext dc = new NWindDataContext())  
              {  
       
                       var q =  
                       (from c in dc.GetTable<Customer>()  
                       where c.CustomerID == "AAAAA"  
                       select c).Single<Customer>();  
       
                       foreach (Order ord in q.Orders)  
                       {  
                                 dc.GetTable<Order>().DeleteOnSubmit(ord);  
       
                                 foreach (Order_Detail od in ord.Order_Details)  
                                 {  
                                           dc.GetTable<Order_Detail>().DeleteOnSubmit(od);  
                                 }  
                        }  
                        dc.GetTable<Customer>().DeleteOnSubmit(q);  
                        dc.SubmitChanges();  
              }  
              UpdateDataGrid();  
    }  
    catch (Exception ex)  
    {  
              MessageBox.Show(ex.Message);  
    }

In looking at this example, to delete the customer along with the related orders and order details, the code first selects the matching customer by the customer ID field (it's the primary key).  Once a match is found, the code loops through the orders related to each customer and marks them for deletion using the DeleteOnSubmit call.
 
Further, since another relationship exists between the order and order details, the code loops through all of the order details associated with the order and marks them for deletion as well.  Lastly, the customer itself if marked for deletion and then Submit Changes is called on the data context.  The order in which the entities are marked for deletion does not matter, LINQ to SQL sorts that out during the execution of the Submit Changes call based upon the configuration of the foreign keys.

Handling the Cascading Delete from within SQL Server
It is possible to manage the cascading deletes entirely from within SQL Server.  To do this, one need only set the delete rule for the foreign key relationship to cascade.

If you have a database diagram built, the easiest way to set the delete rule is to merely open the diagram, click on the foreign key relationship within the diagram, and then open the INSERT and UPDATE property to expose the Delete Rule property, and then set the Delete Rule property to Cascade as shown in Figure 3.
 
To repeat the example of deleting a customer with related orders, if we were to set all of the constraint delete rules to cascade we could delete a customer with this bit of code:
    try  
    {  
              using (NWindDataContext dc = new NWindDataContext())  
              {  
                       var q =  
                       (from c in dc.GetTable<Customer>()  
                       where c.CustomerID == "AAAAA"  
                       select c).Single<Customer>();  
       
                       dc.GetTable<Customer>().DeleteOnSubmit(q);  
                       dc.SubmitChanges();  
              }  
              UpdateDataGrid();  
    }  
    catch (Exception ex)  
    {  
              MessageBox.Show(ex.Message);  
    }

As you can see in this example code, there was no need to bother with marking each member of an entity set for deletion as in this case SQL Server was instructed on how to deal with a deletion of the customer or order records.  As a result, deleting the customer also results in the deletion of the related records contained in the Order and Order Details tables.
 
Handling the Cascading Delete From within SQL Server
It is also possible to set the foreign key field in the entity sets to nullable and then set the delete rule for that field to "Set Null".  One could also set a default value for the field and set the delete rule to "Set Default".
 
Either approach could be useful if there was a need to delete (in this example) a customer record but retain the order and order detail records.  Either approach could be handled in a manner similar to that used in the previous solution alternative.  Setting the foreign key value to nullable is probably not advisable but it is a workable alternative.
 
Handling the Cascading Delete With a Stored Procedure
One may create or add a stored procedure that will accomplish the cascading delete and evoke that stored procedure using LINQ to SQL.  Stored procedures added to the designer may be evoked directly from the data context, for example, if we had stored procedure called DeleteCustomer that took the customer ID as an argument and handled the cascading deletes, we could do something like this:
    Using(NwindDataContext dc = new NwindDataContext())  
    {  
         dc.DeleteCustomer("AAAAA");  
    }

Cascading deletes are not new to LINQ to SQL; it is the same issue it has always been.  In this article, I have described a few approaches to dealing with cascading deletes from within the code and from the SQL Server side but as is true with many things in .NET, there are several other ways to accomplish such action from within LINQ to SQL.

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MARS- Multiple Active Result Sets is a feature supported in sqlserver 2005. In this method having a single connection to the database, our applications can execute. Multiple queries and stored procedures and divides each result of a query or stored procedure as active results. These results are forward-only, read-only data. Previous to MARS, it was required multiple database connections to retrieve data for a separate query or stored procedure, but within a single connection to the database, it's possible to retrieve all data. This helps your application performance and code management greatly.

In the previous methods each sqlconnection object must be disposed of correctly and datareaders associated with each query must be disposed of. Otherwise, it will lead to some errors like "There is already an open DataReader associated with this Connection- error".

With the introduction of MARS in Sqlserver2005 bye-bye to all these problems and performance bottlenecks.

Let's start the Implementation

Settings

You must change your connection string as follows :

String connectionString = "Data Source=TestServer;" +"Initial Catalog=Pubs;IntegratedSecurity=SSPI;" + "MultipleActiveResultSets=True";

MARS is disabled by default on the Connection object. You have to enable it with the addition of MultipleActiveResultSets=true in your connection string.

Program:

This c# code snippet demonstrates the use of MARS.

using System.Data;  
using System.Data.SqlClient;  

public class MARSdemo {  
Public static void Main() {  
    String MarsConnectionStr = "Data Source=TestServer;" + "Initial Catalog=Pubs;IntegratedSecurity=SSPI;" + "MultipleActiveResultSets=True";  
    string Mars_Command_Str1 = "select * from Salary;";  
    string Mars_Command_Str2 = "select * from Employees;";  

    SqlCommand cmd1 = new SqlCommand(Mars_Command_Str1, MarsConnectionStr);  
    SqlCommand cmd2 = new SqlCommand(Mars_Command_Str1, MarsConnectionStr);  
    SqlDataReader rdr1 = null;  
    SqlDataReader rdr2 = null;  
    try {  
        con.Open();  
        rdr1 = cmd1.ExecuteReader();  
        rdr2 = cmd2.ExecuteReader();  
    } catch (SqlException ex) {} finally {  
        if (con.State == ConnectionState.Open) {  
            con.Close();  
        }  
        rdr1.Close();  
    }  
}  
}

If you try to execute this code with sqlserver 2000 or lower versions, u will get an InvalidOperationException and the following error message.

"There is already an open DataReader associated with this Command which must be closed first."

MARS works on the concept of "Multiplexing" and "interleaving". SQL's Select statement is a multiplexed enabled statement. These multiplexed enabled statements can pause its execution in between and allow a non-multiplexed statement to execute like an INSERT statement.

For example, consider you are retrieving 1 million records using a select statement and in between an insert query comes via a MARS-enabled application under the same connection object, then select statement pauses until this insert operation completes and afterward resumes execution.

Note: Managed code (stored procedures, functions, triggers) can't be multiplexed.

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