Question

I am a new and am having some trouble with joining two tables.
table1: (topicID, questionID) where topicID is the primary key. For each topicID, there are many questionID’s.

Now, I have a table2 with questioIDs and I want to get all those topicID’s from table1 which have atleast one entry for each questionID in table2.

I would appreciate any help.

create table table1(
    topicID int,
    questionid int)
create table table2
(
    questionid int
)
insert into table1
select 1,1
union all
select 2,1
union all
select 2,2
union all
select 2,4
union all
select 1,2
union all
select 1,6

insert into table2 
select 1
union all
select 2
union all
select 6

Using table1 and table2 above, the query should return topicID as 2 as only this has atleast one entry for each questionID’s in table2.

Thanks

Answer 1

The relational operator you require is division, popularly known as “the supplier who supplies all parts”.

Because your spec states “has at least one entry for each questionID”, I think you should be looking at division with remainder.

p.s. this is not a topic you’ll find “on Page 1 of almost any SQL reference”, rather it is one of the more obscure relational operators!