Standard Deviation Without stddev | Dataford Interview Questions

How would you get the standard deviation of a column in SQL without using stddev() function?

Asked in the Technical round stage. Using the provided order tables, calculate the sample standard deviation of item values for delivered orders, excluding NULL values.

Output

Return one row with one column named standard_deviation.
Round the result to six decimal places.
Return NULL if fewer than two valid values exist.

Schema

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
order_status	VARCHAR(30)	Current order status

order_items

Column	Type	Description
item_idPK	INT	Unique order item identifier
order_id	INT	Referenced order identifier
item_value	NUMERIC(10,2)	Value of the order item

Your question is Standard Deviation Without stddev. Start with the requirements and the two tables in the Question tab.

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Problem