Sams Teach Yourself SQL in 24 Hours, Third Edition By Ronald R. Plew, Ryan K. Stephens
Table of Contents
Hour 9. Summarizing Data Results from a Query
Aggregate functions can be very useful and are quite simple to use. You have 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, but more follow. Aggregate functions can also be used for group values, which is 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.
