In this chapter, you’ll learn all about a concept in SQL and databases called “null.” In the sample table you’ve been using, every record has a value for every column. However, when working with real databases, this is not always the case. The concept of “null” is used when data is not known.
Missing Data
In a real database, there could be a situation where data is missing. This could be deliberately (we don’t know what the value is), or some kind of bug (there should be a value but there isn’t). Tables in a database don’t require you to store a value in every row and column. ...
