Find common values (Intersection) from one column of a table depending on the given values of second column of same table

Question

I've following table which specifies the areas where suppliers deliver their products, with three columns as

ID   Supp_ID   Area_ID
1      a         P
2      a         R
3      a         T
4      a         s
.      .         .
.      .         .
5      b         R
6      b         T
7      b         V
.      .         .
.      .         .
8      c         Z
9      c         R
10     c         P
11     c         T
.      .         .
.      .         .
.      .         .

Now I want such a stored procedure such that if I pass Supp_IDs a,b,c to the SP, it should return me the Area_IDs R,T which are common in all the 3 suppliers. In short I've to perform intersection of Area_IDs for given Supp_IDs.

Currently what I am trying is as:

select Area_ID from Table_name where Supp_ID=a
INTERSECT
select Area_ID from Table_name where Supp_ID=b
INTERSECT
select Area_ID from Table_name where Supp_ID=c

The above code is good when I know there is exact three Supp_IDs But I am not able to find how to use above logic at run when there will be different numbers of Supp_IDs.

Now I am not able to find how should I write above SP.

Thanks in advance.

Answer 1

select Area_ID
from Table1
where Supp_ID in ('a', 'b', 'c')
group by Area_ID
having count(distinct Supp_ID) = 3

Or, to clarify where 3 comes from:

declare @Filter table(ID nchar(1) primary key)

insert into @Filter values ('a'), ('b'), ('c')

select a.Area_ID
from Table1 as a
where a.Supp_ID in (select t.ID from @Filter as t)
group by a.Area_ID
having count(distinct Supp_ID) = (select count(*) from @Filter)

sql fiddle demo

Answer 2

Use the following query. This will get all unique area ids for each supplier and select only those that are present N times.

DECLARE @param TABLE (supp_id int)

insert into @param values (1),(2),(3)

select Area_ID from 
    (select Area_ID from table_name t
    inner join @param p on p.supp_id = t.supp_id) x
group by x.Area_ID
having count(*) = (select count(*) from @param)