Understanding of nested SQL in C#

Understanding of nested SQL in C#

using (var connection = new SqlConnection(...))
{
string sql = "SELECT * FROM tableA";
using (var command = new SqlCommand(sql,connection))
{
using (var reader = command.ExecuteReader(...))
{
//***************Sample Start
string sql2 = "INSERT into tableB(column1)
VALUES('"+reader["column1"]+"')";
using (var command2 = new SqlCommand(sql2,connection))
{
...
}
//***************Sample End
}
}
}
By using the above code snippet, I believe its the best practice to deal
with SQL in C#. Now after I retrieve a list of records from tableA, for
each of the row I would like to insert into tableB. However, its throwing
me an exception saying that There is already an open DataReader associated
with this Command which must be closed first. I know this problem can be
solved by creating another method and insert into the table from there,
I'm wondering if there is any other way. Thanks for any input.