title: What is causing "Subquery returned more than 1 value..." error?
body: <p>I dont have any idea why am i getting this error :-</p>
  
  <pre><code>Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, &lt;, &lt;= , &gt;, &gt;= or when the subquery is used as an expression.
  The statement has been terminated.
  </code></pre>
  
  <p>I was trying to run this query:-</p>
  
  <pre><code>ALTER TABLE Test1 NOCHECK CONSTRAINT ALL
  ALTER TABLE Test2 NOCHECK CONSTRAINT ALL
  
  
  UPDATE Test1 
  SET ID= '05f6c6b4-63ff-45b2-a5e2-920d5dce3e45' 
  WHERE ID = '05e6c6b4-63ff-45b2-a5e2-920d5dce3e45'; 
  UPDATE Test2 
  SET ID = '05f6c6b4-63ff-45b2-a5e2-920d5dce3e45' ,
  SpecID = NULL ,
  RefLastName = 'Dummy' ,
  RefFirstName = 'First Name' ,
  RefMiddleName = NULL ,
  RefPhone1 = '111444444' ,
  RefPhone2 = '2121222' ,
  RefFax = '222222' ,
  RefEmail = 'xxxxxxx@hotmail.ca' 
  WHERE 
  RefID = '05e6c6b4-63ff-45b2-a5e2-920d5dce3e45' 
  
  ALTER TABLE Test1 WITH CHECK CHECK CONSTRAINT ALL
  ALTER TABLE Test2 WITH CHECK CHECK CONSTRAINT ALL
  </code></pre>