MySQL COUNT(), AVG() and SUM() Functions

The COUNT() function returns the number of rows that matches a specified criterion.

SELECT COUNT(column_name)
FROM table_name
WHERE condition;

The AVG() function returns the average value of a numeric column.

SELECT AVG(column_name)
FROM table_name
WHERE condition;

The SUM() function returns the total sum of a numeric column.

SELECT SUM(column_name)
FROM table_name
WHERE condition;

Demo Database

Below is a selection from the “Products” table in the Northwind sample database:

ProductID	ProductName	SupplierID	CategoryID	Unit	Price
1	Chais	1	1	10 boxes x 20 bags	18
2	Chang	1	1	24 – 12 oz bottles	19
3	Aniseed Syrup	1	2	12 – 550 ml bottles	10
4	Chef Anton’s Cajun Seasoning	2	2	48 – 6 oz jars	22
5	Chef Anton’s Gumbo Mix	2	2	36 boxes	21.35

The following SQL statement finds the number of products:

SELECT COUNT(ProductID)
FROM Products;

Note: NULL values are not counted.

The following SQL statement finds the average price of all products:

SELECT AVG(Price)
FROM Products;

Note: NULL values are ignored.

Below is a selection from the “OrderDetails” table in the Northwind sample database:

OrderDetailID	OrderID	ProductID	Quantity
1	10248	11	12
2	10248	42	10
3	10248	72	5
4	10249	14	9
5	10249	51	40

The following SQL statement finds the sum of the “Quantity” fields in the “OrderDetails” table:

SELECT SUM(Quantity)
FROM OrderDetails;

Note: NULL values are ignored.