Question

I believe in JAVA we can set the data reader to point to the 1st row of it’s result set. I have a SQLDataReader that has over 20 columns and I need to pre-process some columns and calculate some values before I use the entire result set. Is it possible to re-read the data reader after reading it for the first time to get just selected columns? Or will I need to store the results in a data table and read from it later?

Answer 1

From the MSDN docs at http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.aspx

Provides a way of reading a forward-only stream of rows from a SQL Server database.

You can read one row at a time, but you cannot go back to a row once you’ve read the next row.

You can read columns in a row in any order, any number of times, and skip fields if you want.

while (reader.Read())
{
    var a = reader[2];   // you can skip fields
    var b = reader[0];   // you don't have to read the fields in order
    var c = reader[2];   // you can re-read fields
}