Step-by-step approach may work for you, too. It is easier to write the query if I figure out each clause before moving on to the next one. Let’s take a look at the parts, known as clauses, of an aggregate query. SELECT COUNT(*), MAX(Freight), EmployeeID Of a group is less than 800 or the ShippedDate of an order IS NULL. Rows are filtered out of the results if the maximum freight The following query from the Northwind database finds the count of orders and the maximumįreight grouped by EmployeeID. The DISTINCT argument, when used within an aggregate expression, will cause it to operate on non-null unique values.The aggregate functions ignore NULL values.COUNT can be used with an asterisk (*) to give the count of the rows by group or entire set of results.The COUNT function can operate on any column except for text, ntext or image columns.The functions MIN and MAX will work on numeric, character and date columns.The functions AVG and SUM will only operate on numeric columns.Keep the following in mind when working with these aggregate functions. The most commonly used aggregateįunctions are AVG, COUNT, MIN, MAX and SUM. However, in some cases they will work on the entire table. What are aggregate functions?Īggregate functions are used to summarize data in queries. It is intended to cover the basics of using aggregate expressions and does This article will explain how to write queries using aggregates and, hopefully,Ĭlear up the confusion. Query writers are frequently confused about the difference between the WHEREĬlause and the HAVING clause or have trouble figuring out which columns to include in the It takes some practice to become proficient in their use. The use of aggregate functions in queries is a popular and powerful feature of the SQL

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