Learn SQL in a Month of Lunches MEAP V08 by copyright-2023-manning-publications.html

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As noted earlier, null values are some of the most misunderstood concepts in databases. Put simply, NULL values are literally nothing. They represent the absence of data. This seems simple to understand, but because null values are not values like 30 or Arizona or May 12th of 2012, they need to be considered differently from other values when querying data.

Let’s look at an example by reviewing all the columns in the author table. Executing the following query will return all the columns for all 11 records in the author table. One of the first things you might notice is the MiddleName column, which has quite a few values that say NULL. Not everyone has a middle name, so the absence of a middle name for any author is represented by NULL. The Workbench tries to bring this to your attention by making null values appear different from other values we’ve seen so far, in that they are shown in white text with a smaller font size and a dark background color:

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