How to code aggregate functions

Function syntax	Resullt
AVG(expression)	The average of the non-NULL values in the expression.
SUM(expression)	The total of the non-NULL values in the expression.
MIN(expression)	The lowest non-NULL value in the expression.
MAX(expression)	The highest non-NULL value in the expression.
COUNT(expression)	The number of non-NULL values in the expression.
COUNT(*)	The number of rows selected by the query.

       SELECT COUNT(*) AS productCount 
       FROM products;
      

      SELECT COUNT(*) AS totalCount, COUNT(shipDate) AS shippedCount 
      FROM orders;
      

      SELECT MIN(listPrice) AS lowestPrice, MAX(listPrice) AS highestPrice, AVG(listPrice) AS averagePrice 
      FROM products;
      

      SELECT SUM(itemPrice * quantity – discountAmount) AS ordersTotal 
      FROM orderItems;
      

Description

• Aggregate functions perform calculations on the values in a set of selected rows. You specify the values to be used in the calculation by coding an expression as the argument.
• In many cases, the expression for an aggregate function is just the name of a column, but it can also be a calculated value that operates on the values in two or more columns.
• A SELECT statement that includes an aggregate function can be called a summary query.
• If you code an aggregate function in the SELECT clause, the SELECT clause can’t include non-aggregate columns from the base table.