C# : Filling a DataTable from a SqlDataReader

The following code snippet shows you how to fill a DataTable from an SqlDataReader with only a few lines of code.

private DataTable GetDataTable()
{
  string sql = "SELECT * FROM MyTable";
  using (SqlConnection myConnection = new SqlConnection(connectionString))
  {
    using (SqlCommand myCommand = new SqlCommand(sql, myConnection))
    {
      myConnection.Open();
      using (SqlDataReader myReader = myCommand.ExecuteReader())
      {
        DataTable myTable = new DataTable();
        myTable.Load(myReader);
        myConnection.Close();
        return myTable;
      }
    }
  }
}

This code executes a DataReader (a SqlDataReader in this case, but you can also use other types, like an OleDbDataReader). It then passes this open reader into the Load method of the DataTable that takes care of copying the data from the reader into the DataTable.

Referenced from : here

SQL Server : Display rows as columns

Let’s start with a fictional scenario.

In this case we have lots of vendors who report in their daily income to us, for this we have a simple table that looks like this.

create table DailyIncome(VendorId nvarchar(10), IncomeDay nvarchar(10), IncomeAmount int)

--drop table DailyIncome

Nothing odd here, just the Vendor id, the day of the week they are referring to and what the income on that day was.

So let’s fill it with some data.

insert into DailyIncome values ('SPIKE', 'FRI', 100)

insert into DailyIncome values ('SPIKE', 'MON', 300)

insert into DailyIncome values ('FREDS', 'SUN', 400)

insert into DailyIncome values ('SPIKE', 'WED', 500)

insert into DailyIncome values ('SPIKE', 'TUE', 200)

insert into DailyIncome values ('JOHNS', 'WED', 900)

insert into DailyIncome values ('SPIKE', 'FRI', 100)

insert into DailyIncome values ('JOHNS', 'MON', 300)

insert into DailyIncome values ('SPIKE', 'SUN', 400)

insert into DailyIncome values ('JOHNS', 'FRI', 300)

insert into DailyIncome values ('FREDS', 'TUE', 500)

insert into DailyIncome values ('FREDS', 'TUE', 200)

insert into DailyIncome values ('SPIKE', 'MON', 900)

insert into DailyIncome values ('FREDS', 'FRI', 900)

insert into DailyIncome values ('FREDS', 'MON', 500)

insert into DailyIncome values ('JOHNS', 'SUN', 600)

insert into DailyIncome values ('SPIKE', 'FRI', 300)

insert into DailyIncome values ('SPIKE', 'WED', 500)

insert into DailyIncome values ('SPIKE', 'FRI', 300)

insert into DailyIncome values ('JOHNS', 'THU', 800)

insert into DailyIncome values ('JOHNS', 'SAT', 800)

insert into DailyIncome values ('SPIKE', 'TUE', 100)

insert into DailyIncome values ('SPIKE', 'THU', 300)

insert into DailyIncome values ('FREDS', 'WED', 500)

insert into DailyIncome values ('SPIKE', 'SAT', 100)

insert into DailyIncome values ('FREDS', 'SAT', 500)

insert into DailyIncome values ('FREDS', 'THU', 800)

insert into DailyIncome values ('JOHNS', 'TUE', 600)

Now, if we select out the flat data that we have, we will get the following:

VendorId   IncomeDay  IncomeAmount

---------- ---------- ------------

SPIKE      FRI        100

SPIKE      MON        300

FREDS      SUN        400

SPIKE      WED        500

SPIKE      TUE        200

JOHNS      WED        900

SPIKE      FRI        100

JOHNS      MON        300

SPIKE      SUN        400

...

SPIKE      WED        500

FREDS      THU        800

JOHNS      TUE        600

A lot of data that it is hard to make something useful of, for example, say that we would like to know what the average income is for each vendor id?

Or what the maximum income is for each day for a particular vendor? Enter the pivot table.

To find the average for each vendor, run this query:

select * from DailyIncome

pivot (avg (IncomeAmount) for IncomeDay in ([MON],[TUE],[WED],[THU],[FRI],[SAT],[SUN])) as AvgIncomePerDay

Outcome:

VendorId   MON         TUE         WED         THU         FRI         SAT         SUN

---------- ----------- ----------- ----------- ----------- ----------- ----------- -----------

FREDS      500         350         500         800         900         500         400

JOHNS      300         600         900         800         300         800         600

SPIKE      600         150         500         300         200         100         400

The find the max income for each day for vendor SPIKE, run this query:

select * from DailyIncome

pivot (max (IncomeAmount) for IncomeDay in ([MON],[TUE],[WED],[THU],[FRI],[SAT],[SUN])) as MaxIncomePerDay

where VendorId in ('SPIKE')

Outcome:

VendorId   MON         TUE         WED         THU         FRI         SAT         SUN

---------- ----------- ----------- ----------- ----------- ----------- ----------- -----------

SPIKE      900         200         500         300         300         100         400

The short story on how it works using the last query.

select * from DailyIncome                                 -- Colums to pivot

pivot (

   max (IncomeAmount)                                                    -- Pivot on this column

   for IncomeDay in ([MON],[TUE],[WED],[THU],[FRI],[SAT],[SUN]))         -- Make colum where IncomeDay is in one of these.

   as MaxIncomePerDay                                                     -- Pivot table alias

where VendorId in ('SPIKE')                               -- Select only for this vendor


The above post is taken from Pivot tables in SQL Server.