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copied!<p>With the .NET 3.0 requirement, the Intersect LINQ extension method is not available, but you can provide your own extension method.</p> <p>All <em>you</em> need is the <code>MatchingRows</code> extension method (see below in the demo code) and then do:</p> <pre><code> IEnumerable<DataRow> unchangedZipCodes = dtExistingZipCodeInDB.MatchingRows(dtCSVExcelSource, "ZipCode"); </code></pre> <p>Then you can loop over unchangedZipCodes, which will contain only those rows with ZipCodes in common between dtExistingZipCodeInDB and dtCSVExcelSource.</p> <p>Below is demo code I wrote using LINQPad. I love <a href="http://www.linqpad.net/" rel="nofollow">LINQPad</a> -- it's great for proof of concept or scratchpadding/sandboxing some code quickly. But it is not <em>required</em> for the solution to this question. </p> <pre><code>void Main() { string colname = "ZipCode"; var dt = new DataTable(); dt.Columns.Add(colname, typeof(string)); dt.Rows.Add(new [] { "12345" } ); dt.Rows.Add(new [] { "67890" } ); dt.Rows.Add(new [] { "40291" } ); var dt2 = new DataTable(); dt2.Columns.Add(colname, typeof(string)); dt2.Rows.Add(new [] { "12345" } ); dt2.Rows.Add(new [] { "83791" } ); dt2.Rows.Add(new [] { "24520" } ); dt2.Rows.Add(new [] { "48023" } ); dt2.Rows.Add(new [] { "67890" } ); /// With .NET 3.5 LINQ extensions, it can be done inline. // var results = dt.AsEnumerable() // .Select(r => r.Field<string>(colname)) // .Intersect(dt2.AsEnumerable() // .Select(r => r.Field<string>(colname))); // Console.Write(String.Join(", ", results.ToArray())); var results = dt.MatchingRows(dt2, colname); foreach (DataRow r in results) Console.WriteLine(r[colname]); } public static class Extensions { /// With .NET 3.0 and no LINQ, create an extension method using yield. public static IEnumerable<DataRow> MatchingRows(this DataTable dt, DataTable dtCompare, string colName) { foreach (DataRow r in dt.Rows) { if (dtCompare.Select(String.Format("{0} = {1}", colName, r[(colName)])).Length > 0) yield return r; } } } </code></pre> <p>Outputs:</p> <pre><code> 12345 67890 </code></pre>

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