How do you implement a SQL query for counting groups?

The GROUP BY clause in SQL can be used to group data and the COUNT function can be used to calculate the number of records in each group.

For example, let’s say we have a table named “orders” with the fields order_id, customer_id, and order_date. If we want to group by customer_id and calculate the number of orders for each customer, we can use the following SQL query:

SELECT customer_id, COUNT(*) as order_count
FROM orders
GROUP BY customer_id;

The above query will return a result set with two columns: customer_id and order_count. Each row represents a different customer, with order_count indicating the number of orders for that customer.

Please note that the COUNT(*) function is used to calculate the number of records in each group. To calculate the number of non-null values in a specific column, you can use COUNT(column_name).

You can also use the HAVING clause to filter the results, for example showing only customers with more than 5 orders.

SELECT customer_id, COUNT(*) as order_count
FROM orders
GROUP BY customer_id
HAVING order_count > 5;