mysql 在最后一行的多列中求和值的最佳方法

Question

I have a table:

Product Category	Number Purchased	Total Discount $	Total Price	Total Sales
car 1	1	100	1000	900
car 2	2	200	2000	1800
car 3	9	900	10000	9100
car 4	null	null	null	null

SELECT
    categ.category_name AS 'Product Category',
    SUM(order.quantity) AS 'Number Purchased',
    SUM(order.discount) AS 'Total Discount $',
    SUM(order.price) AS 'Total Price',
    (SUM(products.price) - SUM(order.discount)) AS 'Total Sales'
FROM
    products
LEFT JOIN
    orders USING (product_id)
LEFT JOIN
    categ USING (category_id)
GROUP BY
    categ.category_id
ORDER BY
    categ.category_name

I'm trying to figure out the best way to produce the sum of the columns in the last row, demonstrated below:

Product Category	Number Purchased	Total Discount $	Total Price	Total Sales
car 1	1	100	1000	900
car 2	2	200	2000	1800
car 3	9	900	10000	9100
car 4	null	null	null	null
null	12	1200	13000	11800

so far I've tried:

SELECT
    categories.category_name AS 'Product Category',
    SUM(order_items.quantity) AS 'Number Purchased',
    SUM(order_items.discount_amount) AS 'Total Discount $',
    SUM(order_items.item_price) AS 'Total Price',
    (SUM(order_items.item_price) - SUM(order_items.discount_amount)) AS 'Total Sales'
FROM
    products
LEFT JOIN
    orders USING (product_id)
LEFT JOIN
    categories USING (category_id)
GROUP BY
    categories.category_id
 
UNION ALL

SELECT  
    NULL, 
    SUM('Number Purchased'), 
    SUM('Total Discount $'), 
    SUM('Total Price'),
    SUM('Total Sales')
FROM
    products
LEFT JOIN
    orders USING (product_id)
LEFT JOIN
    categ USING (category_id)
GROUP BY
    categ.category_id
ORDER BY
    categ.category_name

doesn't seems to be working, any suggestions?

Answer 1

You can do that programatically in your application, that might be the fastest implementation. If you really want to aggregate in MySQL (which executes a second sub-query) and do UNION ALL , then just fix the second part.

You don't need to GROUP BY there:

SELECT
    categories.category_name AS 'Product Category',
    SUM(order_items.quantity) AS 'Number Purchased',
    SUM(order_items.discount_amount) AS 'Total Discount $',
    SUM(order_items.item_price) AS 'Total Price',
    (SUM(order_items.item_price) - SUM(order_items.discount_amount)) AS 'Total Sales'
FROM
    products
LEFT JOIN
    orders USING (product_id)
LEFT JOIN
    categories USING (category_id)
GROUP BY
    categories.category_id
ORDER BY
    categ.category_name
 
UNION ALL

SELECT  
    NULL, 
    SUM(order_items.quantity),
    SUM(order_items.discount_amount),
    SUM(order_items.item_price),
    SUM(order_items.item_price) - SUM(order_items.discount_amount)
    products
LEFT JOIN
    orders USING (product_id)
LEFT JOIN
    categ USING (category_id)

Answer 2

Using UNION does not enforce the sorting order by the ORDER BY clause unfortunately. Try using with rollup in the group by clause:

SELECT
    categ.category_name AS 'Product Category',
    SUM(order.quantity) AS 'Number Purchased',
    SUM(order.discount) AS 'Total Discount $',
    SUM(order.price) AS 'Total Price',
    (SUM(products.price) - SUM(order.discount)) AS 'Total Sales'
FROM
    products
LEFT JOIN
    orders USING (product_id)
LEFT JOIN
    categ USING (category_id)
GROUP BY
    categ.category_id with rollup
ORDER BY
    categ.category_name
;