Aggregate functions are an incredibly useful feature of a RDBMS. You can compute values that summarize many records in the database and only return the result, keeping the source data rows in the DB.
You will be familiar with the COUNT aggregate function from earlier in the book, if not before. This gives you the total number of records returned by your query, but without returning them. You may have read that COUNT(1) performs better than COUNT(*), but this is no longer the case, as SQL Server now optimizes the latter to perform the same as the former.
By default, SQL Server will return a message detailing the count of the records returned, along with the result of every query. You can turn this off by prefixing your query with ...
