Outer join on aggregate query

Question

This is probably a relatively easy question as long as I explain it well enough:
I have two tables:
categorycodes and properties
categorycodes is a lookup table.
both tables have a field catcode that is a char(1) that contains matching data (only numbers 1 - 6)
CREATE
  TABLE CATEGORYCODES
    CATCODE     CHAR(1 BYTE) NOT NULL ,
    DESCRIPTION VARCHAR2(25 BYTE) NOT NULL ,
    CONSTRAINT CATEGORYCODES_PK PRIMARY KEY ( CATCODE ) ENABLE
catcode
1
2
3
4
5
6
The properties table has about 600,000 records. The properties table also has a field called parcelno which is a char(9).  It contains a string of numbers and only numbers.
What I'd like is the following:
catcode, count(*)
1   580
2  300
3 3000
4 235
5 0
6 80
I limited the query results to make sure that there was a set that would not have all the catcodes in it.  I am having trouble getting the one with zero to display.  I know this has to do with how I'm doing the join, but I'm not sure what.
This is a sample of what I've tried:
select i.*
from
(select catcode, count(*)
from properties p
where substr(parcelno,1,3) = '871'
group by catcode) i
right outer join categorycodes cc
on i.catcode = cc.catcode;
I am not worried about situations where catcode is null in properties.  Parcelno can never be null.

Answer 1

Hi,
It looks like your query should work; except you don't want to COUNT (*); that would make every number at least 1.  COUNT (*) means count the total number of rows, no matter what is on them, so it will see the row with just the catcode from the lookup table that doesn't match anything, and count that as 1.  You want to count the number of rows from the properties table, so count some column from the properties that can't be NULL.
Here's a slightly different way
SELECT    c.catcode
,         COUNT (p.catcode)     AS cnt
FROM             categorycodes  c
LEFT OUTER JOIN  properties     p  ON   p.catcode   = c.catcode
                                   AND  SUBSTR ( p.parcelno
                                               , 1
                                               , 3
                                               )    = '871'
If the condition about '871' is part of the join condition, then you don't need a sub-query.
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only) for all tables involved, and also post the results you want from that data.
Point out where the statement above is getting the wrong results, and explain, using specific examples, how you get the right results from the given data in those places.
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