SQL:How to get min Quantity? - sql

Question

I got this problem. When i tried to summarize the min quatity of nations's products and it did not work.
I have 2 tables below
PRODUCT:
ID|NAME |NaID|Qty
-------------------
01|Fruit|JP |50
02|MEAT |AUS |10
03|MANGA|JP |80
04|BOOK |AUS |8
NATION:
NaID |NAME
-------------------
AUS |Australia
JP |Japan
I want my result like this:
ID|NAME |Name|minQty
-------------------
01|Fruit|JP |50
04|BOOK |AUS |8
and i used:
select p.id,p.name, p.NaID,n.name,min(P.Qty)as minQty
from Product p,Nation n
where p.NaID=n.NaID
group by p.id,p.name, p.NaID,n.name,p.Qty
and i got this (T_T):
ID|NAME |NaID|minQty
-------------------
01|Fruit|JP |50
02|MEAT |AUS |10
03|MANGA|JP |80
04|BOOK |AUS |8
Please,Could soneone help me? I am thinking that i am bad at SQL now.

Answer 1

SQL Server 2005 supports window functions, so you can do something like this:
select id,
name,
NaID,
name,
qty
from (
select p.id,
p.name,
p.NaID,
n.name,
min(P.Qty) over (partition by n.naid) as min_qty,
p.qty
from Product p
join Nation n on p.NaID=n.NaID
) t
where qty = min_qty;
If there is more than one nation with the same minimum value, you will get each of them. If you don't want that, you need to use row_number()
select id,
name,
NaID,
name,
qty
from (
select p.id,
p.name,
p.NaID,
n.name,
row_number() over (partition by n.naid order by p.qty) as rn,
p.qty
from Product p
join Nation n on p.NaID = n.NaID
) t
where rn = 1;
As your example output with only includes the NaID but not the nation's name you don't really need the the join between product and nation.
(There is no DBMS product called "SQL 2005". SQL is just a (standard) for a query language. The DBMS product you mean is called Microsoft SQL Server 2005. Or just SQL Server 2005).

Answer 2

In Oracle, you can use several techniques. You can use subqueries and analytic functions, but the most efficient one is to use aggregate functions MIN and FIRST.
Your tables:
SQL> create table nation (naid,name)
2 as
3 select 'AUS', 'Australia' from dual union all
4 select 'JP', 'Japan' from dual
5 /
Table created.
SQL> create table product (id,name,naid,qty)
2 as
3 select '01', 'Fruit', 'JP', 50 from dual union all
4 select '02', 'MEAT', 'AUS', 10 from dual union all
5 select '03', 'MANGA', 'JP', 80 from dual union all
6 select '04', 'BOOK', 'AUS', 8 from dual
7 /
Table created.
The query:
SQL> select max(p.id) keep (dense_rank first order by p.qty) id
2 , max(p.name) keep (dense_rank first order by p.qty) name
3 , p.naid "NaID"
4 , n.name "Nation"
5 , min(p.qty) "minQty"
6 from product p
7 inner join nation n on (p.naid = n.naid)
8 group by p.naid
9 , n.name
10 /
ID NAME NaID Nation minQty
-- ----- ---- --------- ----------
01 Fruit JP Japan 50
04 BOOK AUS Australia 8
2 rows selected.
Since you're not using Oracle, a less efficient query, but probably working in all RDBMS:
SQL> select p.id
2 , p.name
3 , p.naid
4 , n.name
5 , p.qty
6 from product p
7 inner join nation n on (p.naid = n.naid)
8 where ( p.naid, p.qty )
9 in
10 ( select p2.naid
11 , min(p2.qty)
12 from product p2
13 group by p2.naid
14 )
15 /
ID NAME NAID NAME QTY
-- ----- ---- --------- ----------
01 Fruit JP Japan 50
04 BOOK AUS Australia 8
2 rows selected.
Note that if you have several rows with the same minimum quantity per nation, all those rows will be returned, instead of just one as in the previous "Oracle"-query.

Answer 3

with cte as (
select *,
row_number() over (partition by Nation order by qty) as [rn]
from product
)
select * from cte where [rn] = 1