Using WITH clause and INSERT statement in POSTGRESQL - postgresql

Question

There was a question asked several years ago with a similar title (Using WITH clause with INSERT statement in POSTGRESQL), but I need to figure out a more complicated situation.
I've used the example from POSTGRESQL for using a "With" statement (https://www.postgresql.org/docs/current/queries-with.html). Let's say I made a pre-computed table and wanted to insert the output from the query into it (top_region, total_sales, product_units, and product_sales), how would I do that?
Precomputed table
INSERT INTO top (top_region, total_sales, product_units, product_sales)
select top_region, total_sales, product_units, product_sales
from #not sure here
WITH regional_sales AS (
SELECT region, SUM(amount) AS total_sales
FROM orders
GROUP BY region
), top_regions AS (
SELECT region
FROM regional_sales
WHERE total_sales > (SELECT SUM(total_sales)/10 FROM regional_sales)
)
SELECT region,
product,
SUM(quantity) AS product_units,
SUM(amount) AS product_sales
FROM orders
WHERE region IN (SELECT region FROM top_regions)
GROUP BY region, product;
My query
WITH sales_data AS (
SELECT s.customer_id, s.product_id, s.quantity, pr.list_price, pr.category_id, c.state_id
FROM order_products s
INNER JOIN Products pr ON (s.product_id = pr.product_id)
INNER JOIN Customer c ON (s.customer_id = c.customer_id)
),
t_20cat AS (
SELECT category_id, ROW_NUMBER() OVER (ORDER BY SUM(list_price*quantity) DESC) AS "rank", SUM(list_price*quantity) AS total_sales FROM sales_data
GROUP BY category_id ORDER BY total_sales DESC LIMIT 20
),
t_20cust AS (
SELECT customer_id, ROW_NUMBER() OVER (ORDER BY SUM(list_price*quantity) DESC) AS "rank", SUM(list_price*quantity) AS total_sales FROM sales_data
GROUP BY customer_id ORDER BY total_sales DESC LIMIT 20
),
t_20cc AS (
SELECT customer_id, t_20cust.rank as customer_rank, category_id, t_20cat.rank as category_rank FROM t_20cat, t_20cust
)
SELECT t_20cc.*, COALESCE(SUM(sales_data.quantity), 0) AS quantity_sold, COALESCE(SUM(sales_data.list_price*sales_data.quantity), 0) AS dollar_value
FROM t_20cc
LEFT JOIN sales_data ON (
t_20cc.customer_id = sales_data.customer_id AND t_20cc.category_id = sales_data.category_id
)
GROUP BY t_20cc.customer_id, t_20cc.customer_rank, t_20cc.category_id, t_20cc.category_rank
INSERT INTO top_20(customer_id, customer_rank, category_id, category_rank
select category_id, category_rank, category_id, category_rank
from t_20cc
)

Answer 1

Move the other SELECT query into its own CTE (region_summary), then reference that in the INSERT statement's SELECT ... FROM clause:
WITH regional_sales AS (
SELECT
region,
SUM(amount) AS total_sales
FROM
orders
GROUP BY
region
),
top_regions AS (
SELECT
region
FROM
regional_sales
WHERE
total_sales > ( SELECT SUM( total_sales ) / 10 FROM regional_sales )
),
region_summary AS (
SELECT
region,
product,
SUM(quantity) AS product_units,
SUM(amount) AS product_sales
FROM
orders
WHERE
region IN ( SELECT region FROM top_regions )
GROUP BY
region,
product
)
INSERT INTO top ( top_region, total_sales, product_units, product_sales )
SELECT
region AS top_region,
product AS total_sales,
product_units,
product_sales
FROM
region_summary;