MARS vs NextResult - ado.net

Question

I rehydrate my business objects by collecting data from multiple tables, e.g.,
SELECT * FROM CaDataTable;
SELECT * FROM NyDataTable;
SELECT * FROM WaDataTable;
and so on...
(C# 3.5, SQL Server 2005)
I have been using batches:
void BatchReader()
{
string sql = "Select * From CaDataTable" +
"Select * From NyDataTable" +
"Select * From WaDataTable";
string connectionString = GetConnectionString();
using (SqlConnection conn = new SqlConnection(connectionString)) {
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
using (SqlDataReader reader = cmd.ExecuteReader()) {
do {
while (reader.Read()) {
ReadRecords(reader);
}
} while (reader.NextResult());
}
}
}
I've also used multiple commands against the same connection:
void MultipleCommandReader()
{
string connectionString = GetConnectionString();
string sql;
SqlCommand cmd;
using (SqlConnection conn = new SqlConnection(connectionString)) {
conn.Open();
sql = "Select * From CaDataTable";
cmd = new SqlCommand(sql, conn);
using (SqlDataReader reader = cmd.ExecuteReader()) {
while (reader.Read()) {
ReadRecords(reader);
}
}
sql = "Select * From NyDataTable";
cmd = new SqlCommand(sql, conn);
using (SqlDataReader reader = cmd.ExecuteReader()) {
while (reader.Read()) {
ReadRecords(reader);
}
}
sql = "Select * From WaDataTable";
cmd = new SqlCommand(sql, conn);
using (SqlDataReader reader = cmd.ExecuteReader()) {
while (reader.Read()) {
ReadRecords(reader);
}
}
}
}
Is one of these techniques significantly better than the other?
Also, would there be a gain if I use MARS on the second method? In other words, is it as simple as setting MultipleActiveResultSets=True in the connection string and reaping a big benefit?

Answer 1

If the data structure is the same in each table, I would do:
Select *, 'Ca' Source From CaDataTable
union all
Select *, 'Ny' Source From NyDataTable
union all
Select *, 'Wa' Source From WaDataTable

Answer 2

Without actually timing the two versions against one another, you can only speculate....
I hope bet that version 1 (BatchReader) will be faster, since you only get one round-trip to the database. Version 2 requires three distinct round-trips - one each for every query you execute.
But again: you can only really tell if you measure.
Marc
Oh, PS: of course in a real-life scenario it would also help so limit the columns returned, e.g. don't use SELECT * but instead use SELECT (list of fields) and keep that list of fields as short as possible.