Question

The database I’m accessing has two tables I need to query using DB2 SQL, shown here as nametable and addresstable. The query is for finding all of the people with a certain balance due. The addresses are stored in a separate table to keep track of address changes. In addresstable, the latest address is determined by a sequence number (ADDRSEQUENCE). The AddressID field is present in both tables, and is what ties each person to specific addresses. The highest sequence number is the current address. I need that current address for each person and only that one. I know I’m going to have to use MAX somewhere for the sequence number, but I can’t figure out how to position it given the join. Here’s my current query, which of course returns all addresses…

SELECT NAMETABLE.ACCTNUM AS ACCOUNTNUMBER, 
NAMETABLE.NMELASTBUS AS LASTNAME,
NAMETABLE.NAME_FIRST AS FIRSTNAME, 
NAMETABLE.BALDUE AS BALANCEDUE,
ADDRESSTABLE.STREETNAME AS ADDR, 
ADDRESSTABLE.ADDRLINE2 AS 
ADDRLINE2,ADDRESSTABLE.CITYPARISH AS CITY, 
ADDRESSTABLE.ADDRSTATE AS STATE,
ADDRESSTABLE.ZIPCODE AS ZIP, 
ADDRESSTABLE.ADDIDSEQNO AS ADDRSEQUENCE
FROM NAMETABLE JOIN ADDRESSTABLE ON NAMETABLE.ADDRESSID = ADDRESSTABLE.ADDRESSID
WHERE NAMETABLE.BALANCEDUE >= '50.00'

Answer 1

You can do a sub-select on the MAX(ADDRSEQUENCE) like so:

SELECT 
     N.ACCTNUM AS ACCOUNTNUMBER
    ,N.NMELASTBUS AS LASTNAME
    ,N.NAME_FIRST AS FIRSTNAME
    ,N.BALDUE AS BALANCEDUE
    ,A.STREETNAME AS ADDR, 
    ,A.ADDRLINE2 AS 
    ,A.ADDRLINE2
    ,A.CITYPARISH AS CITY, 
    ,A.ADDRSTATE AS STATE,
    ,A.ZIPCODE AS ZIP, 
FROM NAMETABLE AS N 
JOIN ADDRESSTABLE AS A 
  ON N.ADDRESSID = A.ADDRESSID
WHERE N.BALANCEDUE >= '50.00'
  AND A.ADDRSEQUENCE = (
    SELECT MAX(ADDRSEQUENCE)
    FROM ADDRESSTABLE AS A2
    WHERE A.ADDRESSID = A2.ADDRESSID
)

This is pretty quick in DB2.