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

```
-- step-1 Calculating moving average and moving standard deviation
SELECT
operator,
AVG(height) OVER(
PARTITION BY operator
ORDER BY item_no
ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
) AS avg_height,
STDDEV(height) OVER(
PARTITION BY operator
ORDER BY item_no
ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
) AS stddev_height
FROM manufacturing_parts;
```

```
-- step-2 Calculating upper and lower control limits
-- made CTE the previous query
WITH avg AS(
SELECT
operator,
AVG(height) OVER(
PARTITION BY operator
ORDER BY item_no
ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
) AS avg_height,
STDDEV(height) OVER(
PARTITION BY operator
ORDER BY item_no
ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
) AS stddev_height
FROM manufacturing_parts
)
-- actual start step-2
SELECT
avg.*,
avg.avg_height + 3*avg.stddev_height/SQRT(5) AS ucl,
avg.avg_height - 3*avg.stddev_height/SQRT(5) AS lcl
FROM avg;
```

```
-- step-3 Creating an alert to evaluate the manufacturing process
-- copied and recalled step-2 with CTE-1
WITH avg AS(
SELECT
operator,
item_no, -- Added item_no to the SELECT list
height,
AVG(height) OVER(
PARTITION BY operator
ORDER BY item_no
ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
) AS avg_height,
STDDEV(height) OVER(
PARTITION BY operator
ORDER BY item_no
ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
) AS stddev_height
FROM manufacturing_parts
),
-- made another CTE-2 to the previous query again
calcu AS (
SELECT
*,
ROW_NUMBER() OVER (PARTITION BY operator ORDER BY item_no) AS row_num, -- Corrected window function definition to set row_num
avg.avg_height + 3*avg.stddev_height/SQRT(5) AS ucl,
avg.avg_height - 3*avg.stddev_height/SQRT(5) AS lcl
FROM avg
)
-- actual start of step-3, Final query
SELECT
* ,
CASE WHEN height NOT BETWEEN lcl AND ucl
THEN TRUE ELSE FALSE END AS alert
FROM calcu -- calling CTE-2 is enough
WHERE row_num >= 5;
```

```
-- step-3 Creating an alert to evaluate the manufacturing process
-- copied and recalled step-2 with CTE-1
WITH avg AS(
SELECT
operator,
item_no, -- Added item_no to the SELECT list
height,
AVG(height) OVER(
PARTITION BY operator
ORDER BY item_no
ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
) AS avg_height,
STDDEV(height) OVER(
PARTITION BY operator
ORDER BY item_no
ROWS BETWEEN 4 PRECEDING AND CURRENT ROW
) AS stddev_height
FROM manufacturing_parts
),
-- made another CTE-2 to the previous query again
calcu AS (
SELECT
*,
ROW_NUMBER() OVER (PARTITION BY operator ORDER BY item_no) AS row_number, -- Corrected window function definition to set row_number
avg.avg_height + 3*avg.stddev_height/SQRT(5) AS ucl,
avg.avg_height - 3*avg.stddev_height/SQRT(5) AS lcl
FROM avg
)
-- actual start of step-3, Final query
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 calcu -- calling CTE-2 is enough
WHERE row_number >= 5;
```