Sum dataset in SQL with conditional expressions - sql

Question

I'm working with a dataset of items with different values and I would like a SQL query to calculate the total USD value of the dataset.
Example Dataset:
id | type | numOrdered
0 | apple | 1
1 | orange | 3
2 | apple | 10
3 | apple | 5
4 | orange | 2
5 | apple | 1
Consider this dataset of fruit orders. Let's say apples are worth $1 and oranges are worth $2. I would like to know how much total USD in fruit orders we have.
I'd like to perform the same operation as this example Javascript function, but using SQL:
let sum = 0;
for(let fruitOrder of fruitOrders) {
if(fruitOrder.type == "orange"){
sum += fruitOrder.numOrdered*2;
} else {
sum += fruitOrder.numOrdered*1;
}
}
return sum;
So the correct answer for this dataset would be $27 USD total since there are 17 apples worth $1 and 5 oranges worth $2.
I know how to break it down into two distinct queries giving me the number I want split by type
SELECT
sum("public"."fruitOrders"."num"*2) AS "sum"
FROM "public"."fruitOrders"
WHERE "public"."fruitOrders"."type" = 'orange';
which would return $10, the total USD value of oranges
SELECT
sum("public"."fruitOrders"."num") AS "sum"
FROM "public"."fruitOrders"
WHERE "public"."fruitOrders"."type" = 'apple';
which would return $17, the total USD value of apples
I just don't know how to sum those numbers together in SQL to get $27, the total USD value of the dataset.

Answer 1

If you want the values 1 and 2 hardcoded then you can use a CASE statement with SUM():
SELECT
sum(case type
when 'apple' then 1
when 'orange' then 2
end * numordered
) AS "sum"
FROM "public"."fruitOrders"
See the demo.
Result:
| sum |
| --- |
| 27 |