Aggregate functions can be useful and are quite simple to use. In this hour you learned how to count values in columns, count rows of data in a table, get the maximum and minimum values for a column, figure the sum of the values in a column, and figure the average value for values in a column. Remember that NULL values are not considered when using aggregate functions, except when using the COUNT function in the format COUNT(*).
Aggregate functions are the first functions in SQL that you have learned in this book, but more follow in the coming hours. You can also use aggregate functions for group values, which are discussed during the next hour. As you learn about other functions, you see that the syntaxes of most functions are similar to one another and that their concepts of use are relatively easy to understand.