As developers, we all probably know what a NULL is in SQL Server. NULL is not a specific value but it stands for UNKNOWN value. In other words, NULL represents the ‘absence of data’.
The behavior and treatment of NULL in SQL server is very interesting in different context and part of T-SQL language. Let’s have a quick look on how it is treated in different ways by SQL Server.
When you use NULL (UNKNOWN value) in Arithmetic operations or in String Concatenation operations, the result is always UNKNOWN because the value which is being operated is not available or UNKNOWN. So, all the following statements yield the result of NULL: