Introduction"I want to list customers who haven't ordered, but I get zero results," or "The count doesn't match when I exclude cancellations." Among SQL bugs, those caused by NULL are often discovered ...

For those new to data analysis, I will explain how to handle NULL (empty fields), where mistakes are most common in SQL, using concrete examples and results. Understanding NULL will help you solve ...

In SQL, NULL is a special marker that represents missing or undefined data, and comparing values to NULL requires special syntax. Standard comparison operators (=, <>, <, >, <=, >=) do not work as ...