SQL statement using result of aggregate min function to fetch a row - how?

Question

Need help trying to get to something seemingly simple. I'll provide a simple example to illustrate the problem.
I'll be using a simple addresses table with 4 fields.
Create the table:
  CREATE TABLE "ADDRESSES"
   (     "OWNER_NAME" VARCHAR2(20 BYTE),
     "STREET_NAME" VARCHAR2(20 BYTE),
     "STREET_NUMBER" NUMBER
   ) ;populate with 6 rows
Insert into ADDRESSES (OWNER_NAME,STREET_NAME,STREET_NUMBER) values ('FRED','MAIN',1);
Insert into ADDRESSES (OWNER_NAME,STREET_NAME,STREET_NUMBER) values ('JOAN','MAIN',2);
Insert into ADDRESSES (OWNER_NAME,STREET_NAME,STREET_NUMBER) values ('JEAN','MAIN',3);
Insert into ADDRESSES (OWNER_NAME,STREET_NAME,STREET_NUMBER) values ('JACK','ELM',1);
Insert into ADDRESSES (OWNER_NAME,STREET_NAME,STREET_NUMBER) values ('JANE','ELM',2);
Insert into ADDRESSES (OWNER_NAME,STREET_NAME,STREET_NUMBER) values ('JEFF','ELM',3);We now have this:
Select * from addresses
OWNER_NAME           STREET_NAME          STREET_NUMBER         
FRED                 MAIN                 1                     
JOAN                 MAIN                 2                     
JEAN                 MAIN                 3                     
JACK                 ELM                  1                     
JANE                 ELM                  2                     
JEFF                 ELM                  3                     
6 rows selectedNow i wish to group by StreetName, and get a count of houses. At the same time, i'd like to know the first and last house number
    select
    street_name,
    count(*) "NBR HOUSES",
    min(street_number) "First Number",
    max(street_number) "Last Number"
     from addresses
    group by street_name
produces
STREET_NAME          NBR HOUSES             First Number           Last Number           
ELM                  3                      1                      3                     
MAIN                 3                      1                      3                     
2 rows selectedExcellent. Now for the problem. I wish to also list on each line, the owner that lives at the first and/or last house number. Note again, assume that house number and street name is unique
It would seem i have all that i need. Not sure how to get at it.
I tried:
select
    street_name,
    count(*) "NBR HOUSES",
    min(street_number) "First Number",
    max(street_number) "Last Number",
    (Select b.owner_name from addresses b where b.street_number = min(street_number) and b.owner_name = owner_name) "First Owner"
     from addresses
    group by street_nameBut get a sql syntax error, group function not allowed when i add the subselect.
any ideas?
thanks for any help.
Edited by: user6876601 on Nov 19, 2009 7:08 PM
Edited by: user6876601 on Nov 19, 2009 7:30 PM

Answer 1

Hi,
Welcome to the forum!
Getting the highest and lowest number for each street is a fairly simple concept; simpler to describe, and simple to code.
Now you want the owner_name associated with the highest and lowest number, which is a more complicated concept; a little harder to describe, and, unfortunately, much less simple to code, and much, much harder to explain:
select
    street_name,
    count (*)                "NBR HOUSES",
    min (street_number)      "First Number",
    min (owner_name) KEEP (DENSE_RANK FIRST ORDER BY street_number)
                    "First Owner",
    max (street_number)      "Last Number",
    min (owner_name) KEEP (DENSE_RANK LAST ORDER BY street_number)
                    "Last Owner"
     from addresses
    group by street_name
;Notice that I used min for both "First Owner" and "Last Owner". Why is that?
The important keyword in these funtions is the word FIRST or LAST that comes after DENSE_RANK and before ORDER BY. The function at the beginning is merely a tie-breaker.
That is, MIN in this context only refers to what should happen when there is a tie for the first or last in the group. Even if such a thing is impossibe in your data, the generic functions have to have some mechanism for returning a single owner_name when two or more rows have an equal claim to having the highest street_number. For example, if we change Joan's address to 1 Main, then MIN (street_number) is still 1, obviously, but who is the person associated with the minimum street_number: is it Fred or Joan? Both have an equal claim to being the owner with the lowest address on Main Street, but aggregate functions must return a single value, so we have to have some mechanism for tell the system whether to return 'JOAN' or 'FRED'. In this example, I arbitrarily said that in the een of a tie, the lowest name, in alphabetic order, should be returned. In this case, 'FRED' would be returned, since 'FRED' is earlier than 'JOAN' .
Thanks for including the CREATE TABLE and INSERT statements!