Question

I need to filter a table based on ManufacturerID in a stored procedure BUT when a null ManufacturerID is passed in I need all orders.

Can I do this in the WHERE statement so I don;t have to have the entire query written twice in my SP?

Answer 1

WHERE
  @param IS NULL OR field = @param

But note, this gets very inefficient if you scale it up to search multiple columns. (See http://www.sommarskog.se/dyn-search.html)

Example of inefficient scaled up version…

WHERE
      (@param1 IS NULL OR field1 = @param1)
  AND (@param2 IS NULL OR field2 = @param2)
  AND (@param3 IS NULL OR field3 = @param3)