General aggregation queries review

Group by , having, avg, count
https://www.w3schools.com/sql/sql_groupby.asp
https://www.w3schools.com/sql/sql_having.asp
https://www.w3schools.com/sql/func_sqlserver_avg.asp


SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country;


SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
HAVING COUNT(CustomerID) > 5;


SELECT AVG(Price) AS AveragePrice FROM Products;

COUNT (*) vs COUNT(column)

* includes columns with null values
column does not include column with null values

https://stackoverflow.com/questions/3003457/count-vs-countcolumn-name-which-is-more-correct