title: datatype mismatch in criteria expression in MS Access
body: <p>I am creating form in access in which i have to implement cascading combo boxes , data in lower combo box is dependent on its parent value selected by user. Here is form <img src="https://i.stack.imgur.com/5UIfS.png" alt="enter image description here"></p>
  
  <p>on left side is structure of the table and on right side is form. Problem is I am getting error of data type mismatch , unable to understand why this is happening. In the afterupdate event of Diametre of Drill I am populating cutting speed . Whenever I press drop down of Cutting Speed "Datatype mismatch in criteria expression" occurs. Here is code of <strong>afterupdate event of Diametre of Drill</strong></p>
  
  <pre><code>Private Sub cboDiameterDrilling_AfterUpdate()
  cboCuttingSpeedDrilling.RowSource = "Select DISTINCT tblDrilling.cuttingSpeed " &amp; _
  "FROM tblDrilling " &amp; _
  `"WHERE tblDrilling.materials = '" &amp; cboMaterialDrilling.Value &amp; "' AND tblDrilling.diaOfDrill = '` `cboDiameterDrilling.Value ' " &amp; _`
  "ORDER BY tblDrilling.cuttingSpeed;"
  
  End Sub
  </code></pre>
  
  <p>I think problem is in WHERE Clause . Any help would be greatly appreciated. Thank you</p>