Magento MySQL – Calculate average number of orders per day and per month

What is the average number of orders per day?

SELECT AVG( orders_num )
FROM (
SELECT created_at, COUNT( DISTINCT order_id ) orders_num
FROM `sales_flat_order_item`
GROUP BY CAST( created_at AS DATE )
)orders_per_day

What is the average number of orders per month?

SELECT AVG( orders_num ) 
FROM (
SELECT created_at, COUNT( DISTINCT order_id ) orders_num
FROM  `sales_flat_order_item` 
GROUP BY MONTH( created_at )
)orders_per_month

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