Question

I would like to join two tables but to specify that the result should have unique values on one of the columns.

http://sqlfiddle.com/#!2/70ded/4

Instead of

URLID DOMAINID
13    5
9     3
10    3
11    4
12    4
6     2
7     2
8     2
1     1
2     1
3     1
4     1
5     1

I would like to get:

URLID DOMAINID
13    5
9     3
11    4
6     2
1     1

Is it possible doing it and by that creating a faster query?

Answer 1

Your query will not be faster, because you have to remove the duplicates. Here is a MySQL way:

select urlID, domainID
from (<your query>) as t
group by domainID

This uses a MySQL mis(feature) called hidden columns. In most databases, you would use:

select min(urlID), domainID
from (<your query>) as t
group by domainID