I have 3 tables: foods, order_detail, and orders
Here are the records for table foods
:
x
id | name | type
------------------------------
F01 | Omelette | Breakfast
F02 | Burger | Breakfast
F03 | Satay | Lunch
F04 | Fried Rice | Dinner
Here are the records for table order_detail
:
food_id | order_id
-----------------------------
F01 | T01
F04 | T01
F02 | T02
F03 | T03
F03 | T04
And here are the records for orders
table:
order_id | date | qty
---------------------------------
T01 | 2017-05-01 | 2
T02 | 2017-05-02 | 1
T03 | 2017-05-05 | 1
T04 | 2017-05-07 | 1
I want to show count order detail grouped by food type. I expected this result:
type | total_order
-------------------------
Breakfast | 2
Lunch | 2
Dinner | 1
Here is my approach, but it still doesn’t show the expected result.
SELECT
f.type,
(SELECT COUNT(*) FROM order_detail od WHERE f.id = od.food_id) AS total_order
FROM foods f
LEFT JOIN order_detail od ON f.id = od.food_id
GROUP BY f.type
ORDER BY f.id
The result is:
type | total_order
-------------------------
Breakfast | 1
Lunch | 2
Dinner | 1
How can I get the result I want? Thanks in advance!
Advertisement
Answer
Aggregation can work here, but you need to join across all three tables:
SELECT f.type, COUNT(o.order_id) AS total_order
FROM foods f
LEFT JOIN order_detail od ON od.food_id = f.id
LEFT JOIN orders o ON o.order_id = od.order_id
GROUP BY f.type
ORDER BY f.id;
Note that we do a left join across all three tables in order to not drop any food type which might happen to have zero orders.