初学SQL - 可能与JOIN相加

Question

I am relatively new to SQL and have only dealt with very basic statements before.

Table A
- id
- clubid

Table B

• id
• applicationid* (foreign key)id above ^
• n
• p
• k
• mg
• area

What I am trying to do is as follows,

    SELECT * from applications WHERE clubid = $id

Then with the result of this I need to run a query along the lines of,

    SELECT Sum(n), Sum(p), Sum(k), Sum(mg) from productsapplied where area = $area

I know this second statement is wrong because it would be sum'ing each row which isnt possible so I am trying to find a way to link the two queries together. As I said I am a beginner with this, I have looked up on Sum as well as inner joins but can't get my head around it.

If more details are needed, let me know! Many thanks !

Answer 1

I think this may be what you're trying to do:

SELECT Sum(productsapplied.n), Sum(productsapplied.p), Sum(productsapplied.k), Sum(productsapplied.mg)
 FROM productsapplied
 JOIN applications 
 ON productsapplied.applicationid = applications.id 
 WHERE productsapplied.area = $area
 AND applications.clubid = $id