As a developer we always forget how to query for records with NULL values, no matter how many times we do it. It's just weird. Our first instinct is to write the query as such

   SELECT CompanyName, ContactName, ContactTitle,Region
   FROM Customers
   WHERE Region = NULL

But that will not return any results. The funny thing is there's no SQL error so you think that there's no results. However if you change the query to this

   SELECT CompanyName, ContactName, ContactTitle,Region
   FROM Customers
   WHERE Region IS NULL

You see there's plenty of records with Region IS NULL



The reverse is true if you want records that are not NULL you would not write the query like this

   SELECT CompanyName, ContactName, ContactTitle,Region
   FROM Customers
   WHERE Region != NULL

But you want to write the query like this instead

   SELECT CompanyName, ContactName, ContactTitle,Region
   FROM Customers
   WHERE Region IS NOT NULL