If you are new to SQL, this query can look perfectly reasonable at first: SELECT name FROM users WHERE phone = NULL ; Enter fullscreen mode Exit fullscreen mode You have a users table. Some users did not enter their phone number. The phone column looks empty. So you try to find those rows with phone = NULL . But the result comes back empty. The table is not necessarily wrong. The column name may be correct. The query may even look logical. The problem is that NULL is not a normal value. To understand why this query returns nothing, we need to understand what NULL really means. NULL is not an empty value At first, NULL looks like an empty cell. It feels similar to 0 or an empty string. But in SQL, these are different things: 0 -> a number '' -> an empty string NULL -> an unknown or unrecorded state Enter fullscreen mode Exit fullscreen mode 0 is a value. It means the number zero. '' is also a value. It means a string with no characters. But NULL is different.…