SQL Queries for Mere Mortals: A Hands-On Guide to Data Manipulation in SQL, Second Edition

That “Nothing” Value: Null

As you know, a table consists of columns and rows. Each column represents a characteristic of the subject of the table, and each row represents a unique instance of the table’s subject. You can also think of a row as one complete set of column values—each row contains exactly one value from each column in the table. Figure 5-12 shows an example of a typical table.

Figure 5-12. A typical Customers table

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So far we’ve shown how to retrieve information from the data in a table with a SELECT statement and how to manipulate that data by using value expressions. All of this works just fine because we’ve ...