Capturing only the first vendor code (not all) associated with user

Question

Hi All
I have several tables that helps me try to capture the unique number of vendors that are active from the users table as shown below in the SQL script. However, ther is an exception where users may be associated with multiple vendors. I feel that my script captures all associated vendor codes associated with my users. Is there a way of capturing only the first vendor code associated with the user. Thanks for your help.
Gautam
SQL SCRIPT:
select count(distinct(d.vendor_id))
from SSPE.PG_FORM_SUBMIT a, SSPE.SP_USER_AUX b, sspe.pg_supplier_vendor d
where a.SOURCENAME = 'wvInventoryForecast' and
a.PROFILEID = b.ID and
b.SUPPLIER_ID = d.supplier_id and
a.CLOCKTIME between to_date('15-Mar-06','DD-MON-YY') and to_date('04-Apr-06','DD-MON-YY')

Answer 1

you need to have a common criteria to determine which vendor should be selected for an user, if it is by lowest vendor code or if it is the first entered vendor in which case you should have a date (or someother) column to identify which vendor was first associated with the user. In either case you could use the analytic function row_number() to accomplish what you want to do. here is an example
select * from (
select user_id, row_number() over (partition by user_id order by vendor_cd) rn, vendor_cd
from user_table, vendor_table
where <condition>)
where rn=1;
refer online docs for more details on this function (link provided in my earlier post)