SQL COUNT() Function

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

SQL COUNT(column_name) Syntax
The COUNT(column_name) function returns the number of values (NULL values will not be counted) of the specified column:
SELECT COUNT(column_name) FROM table_name
SQL COUNT(*) Syntax
The COUNT(*) function returns the number of records in a table:
SELECT COUNT(*) FROM table_name
SQL COUNT(DISTINCT column_name) Syntax
The COUNT(DISTINCT column_name) function returns the number of distinct values of the specified column:
SELECT COUNT(DISTINCT column_name) FROM table_name
Note: COUNT(DISTINCT) works with ORACLE and Microsoft SQL Server, but not with Microsoft Access.

SQL COUNT(column_name) Example

We have the following "Orders" table:
O_IdOrderDateOrderPriceCustomer
12008/11/121000Hansen
22008/10/231600Nilsen
32008/09/02700Hansen
42008/09/03300Hansen
52008/08/302000Jensen
62008/10/04100Nilsen

Now we want to count the number of orders from "Customer Nilsen".

We use the following SQL statement:
SELECT COUNT(Customer) AS CustomerNilsen FROM Orders
WHERE Customer='Nilsen'

The result of the SQL statement above will be 2, because the customer Nilsen has made 2 orders in total:
CustomerNilsen
2

SQL COUNT(*) Example

If we omit the WHERE clause, like this:
SELECT COUNT(*) AS NumberOfOrders FROM Orders
The result-set will look like this:
NumberOfOrders
6
which is the total number of rows in the table.
SQL COUNT(DISTINCT column_name) Example
Now we want to count the number of unique customers in the "Orders" table.
We use the following SQL statement:
SELECT COUNT(DISTINCT Customer) AS NumberOfCustomers FROM Orders
The result-set will look like this:
NumberOfCustomers
3

which is the number of unique customers (Hansen, Nilsen, and Jensen) in the "Orders" table.

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