NULL is always a challenge for equality, I’ve written about it before. I recently produced some samples for training/explanation of NULL when it comes to IN and NOT IN, and thought I’d include it here.
In data warehousing where aggregation (GROUP BY) is one of the most common things done in queries, we often get the warning: Warning: Null value is eliminated by an aggregate or other SET operation In most cases what is happening is harmless. But what is happening? NULL in aggregation First we have to better understand…
When are two values the same but different? When they are both NULL. Here I compare equality checks, including my datatype neutral method. The Problem Equality (or lack thereof) between values is an easy check. Is 1 = 3, or is 4 <> 5? Many people (and processes) get unexpected results when they try to…