跨多个表聚合的查询

Question

I'm new to SQL, and I'm trying to create a database to manage a small inventory. This is the structure of the db:

DatabaseStructure

I need to create a query that returns the total inventory per material. So, the first step would be to look up for all the batches associated with the material. Second, look up for all the movements associated with each batch. Then, sum the quantity associated with each movement, but depending on the movement type (If it is a good receipt is addition (+), but if it is an inventory withdrawal is subtraction (-)).

Here is an example of the tables with sample data and the desired result.

Table Material

MaterialID	MaterialDescription
1	Bottle
2	Box

Table Batch

BatchID	MaterialID	VendorMaterial	VendorBatch	ExpirationDate
1000	1	2096027	00123456	12/12/2025
1001	1	2096027	00987654	11/11/2026
1002	2	102400	202400E	10/10/2023

Table Movement

MovementID	BatchID	MovementType	Quantity	CreatedBy	CreatedOnDate
1	1000	Good receipt	100	user1@email.com	4/10/2022
2	1000	Inventory withdrawal	20	user2@email.com	4/15/2022
3	1000	Inventory withdrawal	25	user3@email.com	4/17/2022
4	1001	Good receipt	100	user1@email.com	4/20/2022
5	1001	Inventory withdrawal	10	user4@email.com	4/26/2022
6	1002	Good receipt	50	user1@email.com	2/26/2022

Expected query result - total inventory per material:

MaterialDescription	TotalInventory
Bottle	145
Box	50

TotalInventory calculation: for Bottle there are two good receipts movements of 100 and three withdrawals of 20, 25 and 10. So, total inventory will be (100+100)-(20+25+10)=145.

Thanks for your help!

Answer 1

select
    mat.MaterialDescription,
    sum(
        case mov.MovementType
            when 'Good receipt' then 1
            when 'Inventory withdrawal' then -1
            else 0 /* don't know what to do for other MovementTypes */
        end * mov.Quantity
    ) as TotalInventory
from
    Material as mat
    left join Batch as bat on bat.MaterialID = mat.MaterialID
    left join Movement as mov on mov.BatchID = bat.BatchID
group by
    mat.MaterialDescription
;