title: Using a subset of data as the target of a MERGE
body: <p>currently, we're merging against <code>esqlProductTarget</code>:</p>
  
  <pre><code>MERGE esqlProductTarget T
  USING esqlProductSource S
  ON (S.ProductID = T.ProductID)
  WHEN MATCHED 
       THEN UPDATE
       SET    T.Name = S.Name,
              T.ProductNumber = S.ProductNumber,
              T.Color = S.Color
  WHEN NOT MATCHED BY TARGET
  THEN INSERT (ProductID, Name, ProductNumber, Color)
       VALUES (S.ProductID, S.Name, S.ProductNumber, S.Color)
  WHEN NOT MATCHED BY SOURCE
  THEN DELETE;
  </code></pre>
  
  <p>rather than merging against the entire <code>esqlProductTarget</code> target dataset, can we merge against a subset like so:</p>
  
  <pre><code>MERGE (select * from esqlProductTarget where productid&gt;1000) --the only change here is this line
  USING esqlProductSource S
  --etc
  </code></pre>
  
  <p><strong>is it possible to merge a subset of records on the target?</strong></p>