Need Help - System.Data.DataRow to string???

Powershell v4

I wrote a 900 line PS script and thought it was great until I ran it on real data. The SQL query using invoke-sql did not work because the query never finished running with over 1,000,000 records and growing, so I change the program to work on each record instead of each table. This solved the query timeout issue. (Query ran for 15 hours on 1 table and I had to stop it).

However, the program use to export the modified table to a CSV file and now the most I can export is 1 record per CSV file.

I know the $a=$a+$record wont work because $record is just a pointer to where the actual data is stored and it is not a string.

Can you think of a way that I can solve this problem?
If not, I will have to write a CSV file to disk for each record and then merge them all when I'm done with each table. This is the only way I can figure out how to solve this issue.

In my head, I'm thinking there must be a way to create an empty system.data.table? and then add rows to it, but all of the examples I found on the Internet were for C# and I do not know how to convert them to PS, but I did find that in the following example $table has things that are mentioned in the C# code like:
$table.add
$table.clone
$table.copyto
.etc




$table=invoke-sql(...)
foreach ($record in $table)
{
#record.columns are modified here
#done modifying current record
$a = $a + $record
}
#save the table to a CSV file
$a|export-csv ...


Here's some more information in case it helps:

$table.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                      
-------- -------- ----                                     -------                          
True     True     String                                   System.Object                                                                                                

$table.GetTypeCode()
String

$Record.GetType()

IsPublic IsSerial Name                                     BaseType                                                                                                      
-------- -------- ----                                     --------
True     False    DataRow                                  System.Object