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Manufacturing processes for any product is like putting together a puzzle. Products are pieced together step by step, and keeping a close eye on the process is important.

For this project, you're supporting a team that wants to improve how they monitor and control a manufacturing process. The goal is to implement a more methodical approach known as statistical process control (SPC). SPC is an established strategy that uses data to determine whether the process works well. Processes are only adjusted if measurements fall outside of an acceptable range.

This acceptable range is defined by an upper control limit (UCL) and a lower control limit (LCL), the formulas for which are:

The UCL defines the highest acceptable height for the parts, while the LCL defines the lowest acceptable height for the parts. Ideally, parts should fall between the two limits.

Using SQL window functions and nested queries, you'll analyze historical manufacturing data to define this acceptable range and identify any points in the process that fall outside of the range and therefore require adjustments. This will ensure a smooth running manufacturing process consistently making high-quality products.

The data

The data is available in the manufacturing_parts table which has the following fields:

  • item_no: the item number
  • length: the length of the item made
  • width: the width of the item made
  • height: the height of the item made
  • operator: the operating machine
Spinner
DataFrameas
alerts
variable
WITH moving_aggs AS
	(
		SELECT
			operator AS operator
			,ROW_NUMBER() OVER last_five AS row_number
			,height AS height
			,AVG(height) OVER last_five AS avg_height
			,STDDEV(height) OVER last_five AS stddev_height

			FROM public.manufacturing_parts

			WINDOW last_five AS
			(
				PARTITION BY operator 
				ORDER BY item_no 
				ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
			)
	)
, cl_s AS
	(
		SELECT
			*
			,avg_height - 3*(stddev_height/SQRT(5)) AS lcl
			,avg_height + 3*(stddev_height/SQRT(5)) AS ucl
			FROM moving_aggs
	)

SELECT
	operator
	,row_number
	,height
	,avg_height
	,stddev_height
	,ucl
	,lcl
	,CASE
		WHEN height NOT BETWEEN lcl AND ucl THEN TRUE
		ELSE FALSE 
		END AS alert
	
	FROM cl_s
	
	WHERE row_number >= 5