Yesterday I fell into a very simple but dangerous SQL trap.  Can you identify it? Found it?  It’s the comparison to null.  My intention was to get rows where another_column was null, however the query did not do so.  It didn’t give me any results where another_column was null, but didn’t give me any error either.  Why? Null in SQL is not a real value.  Null means “lack of a value” or “unknown”. Anything compared to null leads to an “unknown” result. Therefore, in SQL there are actually three values conditions can evaluate to: true, false, and unknown/null. This is called Continue Reading