The TSQL GROUP
BY clause is used to group data on the basis of columns. You can use group with
or without aggregate function. All this be explained by example below.
The syntax for
the SQL GROUP BY clause is:
SELECT expression1, expression2, ... expression_n,
aggregate_function
(expression)
FROM tables
WHERE conditions
GROUP BY expression1, expression2, ... expression_n;
Using SUM
function
Let say I want
to get total sale amount of a customer. we will write the below query to sales
amount for each customer
SELECT customerid, SUM(totalamount) AS "Total sales"
FROM order_details OD a inner join order o on od.order_id=o.order_id
GROUP BY customerid;
Using COUNT
function
Let say I want
to calculate number of orders made by each customer in store. Then we need to
get the count of orders per customer. Below mentioned will be the query.
SELECT CustomerId, COUNT(*) AS "Number of order"
FROM Order
GROUP BY CustomerID;
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