CASE Statement for Multiple Criteria

Question

Hello,
I need to write a query that will give me a count of customers that fall in three different categories:
< 1 year
1 to 3 years
3 yearsI have written the code to bring me back the 1st set of criteria (< 1 yr). I am using the date connected to a customer's account(s) to return the oldest date attached to an account to put that customer in the appropriate bucket. Below is the code I have for the first piece:
SELECT COUNT(*) AS One_Year_Or_Less
FROM
(SELECT c.lname||', '||c.fname AS Name, MIN(a.contractdate) AS ContractDate
FROM account a, customer c
WHERE a.custnbr = c.custnbr
GROUP BY c.lname, c.fname) yr
WHERE yr.contractdate BETWEEN TO_DATE('03/02/2005', 'MM/DD/YYYY')
AND SYSDATE
The above query runs and returns what I beleive to be an accurate count of customers who fall in the 1 year or less range. My question is; how can I add the criteria of 1 to 3 years and > 3 years to this query. I need to have 3 seperate columns (or 3 seperate rows) that contain the heading of the specific criteria and then the count for that criteria. I was thinking of trying to use a CASE statement but I am unsure of exactly how to do that. Perhaps I could somehow create 3 seperate sub-queries to acheive my goal. Any help with this issue will be greatly appreciated. Thank you.
Dave Y

Answer 1

Here's another way. It will only count those that meet the criteria, otherwise it will sum a 0. If you just want 1 row returned with the counts, there's no need for a GROUP BY
SELECT SUM(CASE
               WHEN contractdate >  add_months(sysdate,-12) THEN 1
               ELSE 0
           END) less_than_1_year
      ,SUM(CASE
               WHEN contractdate >= add_months(sysdate,-36)
               AND  contractdate <= add_months(sysdate,-12) THEN 1
               ELSE 0
           END) from_1_to_3_years
      ,SUM(CASE
               WHEN contractdate <  add_months(sysdate,-36) THEN 1
               ELSE 0
           END) over_3_years
FROM ...