SQL tutorialAggregate functions 

Aggregate functionsSQL aggregate functions allow us to answer the statistical inquiries about a set of data. For example, the users of your sale database system might want know the mean of the sales per year or the maximum and minimum sales of a quarter. The common SQL aggregate functions are AVG, MAX, MIN, COUNT and SUM. AVG Function: This function is used to calculate the average or the
arithmetic mean of data values in a field of a table. TblProduct table:
SELECT AVG(Qty) AS AvgQty FROM TblProduct; Result:
MAX Function: The MAX function is used to find the maximum value among the data value of a field of a table. Its syntax is MAX(fieldname). Example: Find the maximum price of products in the TblProduct. SELECT MAX(UnitPrice) AS Max_price FROM TblProducts; Result:
MIN Function: This function is able to calculate the minimum value of the data value in field of a table. Its syntax is MIN(fieldname). Example: Find the minumum quantity of products in the TblProduct. SELECT MIN(Qty) AS Min_qty FROM TblProducts; Result:
Count Function: This function can count the number of records(rows) in a table. To count all rows in the table although some data in rows are missed, you can use COUNT(*). If you want to count only the rows which contain data you can use COUNT(fieldname) syntax. Example: Count the products that are in the category id of Cat002. SELECT COUNT(ProID) AS Countrows FROM TblProducts WHERE CatID='Cat002'; Result:
SUM Function: This function is used to calculate the total of data values of a field of table. Its syntax is SUM(fieldname). Example: calculate the total quantity of the products in the TblProduct. SELECT SUM(Qty) AS Totalqty FROM TblProduct; Result:

 
