title: Compare two DataTables and select first table records NOT in the second table
body: <p>I have two DataTables that are getting data from two different sources. I would want to have a new DataTable Table3 with ONLY Tables1 rows that do not have matching Table2 rows. My two DataTables have different structures as indicated below. However, they all share the same primary key - CarReg. So, I would like to compare rows using the CarReg column and return all the rows that are in Table1 but NOT in Table2. My returned Table3 DataTable will have same structure as Table1. </p>
  
  <pre><code>Table1.Columns.Add("CarReg", typeof(string));
  Table1.Columns.Add("Site", typeof(string));
  Table1.Columns.Add("Route", typeof(double));
  Table1.Columns.Add("Driver", typeof(string));
  Table1.Columns.Add("StartingDate", typeof(string));
  
  Table2.Columns.Add("CarReg", typeof(string));
  Table2.Columns.Add("SITE DESC", typeof(string));
  Table2.Columns.Add("Route DESC", typeof(double));
  Table2.Columns.Add("Driver", typeof(string));
  Table2.Columns.Add("KILOS", typeof(string));
  </code></pre>
  
  <p>I have tried the below, however, I am getting all records from the first table Table1. I need to get only records that in Table1 but are not in Table2. So, for example if Table1 have 20 records and Tables2 have 15 records, I need to have only the 5 records. Please help. </p>
  
  <pre><code>var recordsNotInB = TableA.AsEnumerable().Select(r =&gt;r.Field&lt;string&gt;("CarReg").Except(TableB.AsEnumerable().Select(r =&gt; r.Field&lt;string&gt;("CarReg")));
  </code></pre>