遍历数据表中的特定列

Question

I have the following code:

using (connection = new SqlConnection("sql connection goes here"))
{
    using(command = new SqlCommand(@"SELECT col1, col2, col3 FROM table1 WHERE col1 = @col1 AND col2 = @col2", connection))
    {
        command.Parameters.Add("@col1", SqlDbType.VarChar, 255).Value = TextBox1.Text;
        command.Parameters.Add("@col2", SqlDbType.VarChar, 255).Value = TextBox2.Text;

        using (dataadapter = new SqlDataAdapter(command))
        {
            using (datatable = new DataTable())
            {
                dataadapter.Fill(datatable);

                int intTest = 0;

                foreach (DataRow row in datatable.Rows)
                {
                    Console.Write(intTest);
                    Console.Write(Environment.NewLine);
                    intTest += 1;

                    // replace this with another database query which uses data from above to loop through further sql queries

                }
            }
        }
    }
}

Works fine. However, I don't understand how to replace that comment section. I basically want to read in rows from a specific column in the foreach loop. How do I enter the values of a specific column into console.write?

Answer 1

A lot of the information from here is applicable: Getting datarow values into a string?

You can get a particular column value using:

row["ColumnName"]

So, for example, if you were writing to the console the value of "FirstName" for every row, it might look like:

foreach (DataRow row in datatable.Rows)
                {
                    Console.Write(intTest);
                    Console.Write(Environment.NewLine);
                    intTest += 1;
                   Console.WriteLine(row["FirstName"]);

                }

The post I referenced above mentions the ItemArray property if that is more applicable to your situation. And @Daniel's comment above about the Field property is good too since my example above assumes you know the type is string, which of course is a big assumption.

Of course, you'll always want to make sure to check that the column exists so you don't get an error. If you're going to build up a large string value by concatenating the value from the column, be sure to use the StringBuilder class so you don't waste resources doing string concatenations over and over.