Question

I have the query below. SOFTWARE_DEVELOPMENT_CYCLE has multiple rows, but I’m interested in the latest.

I would like to rewrite the query so that I don’t use a subquery. I have attempted it with DENSE_RANK LAST ORDERY BY, but to no avail.

Could somebody advise? Thank you.

SELECT SOF.VENDOR, 
       SOF.NAME, 
       LAN.LANGUAGE, 
       SOF.VERSION, 
       SDC.STATUS, 
       SDC.SOF_DC_ID
  FROM SOFTWARE SOF
  JOIN SOFTWARE_LANGUAGES SL 
    ON (SL.SOF_SOF_ID = SOF.SOF_ID)
  JOIN LANGUAGES LAN 
    ON (SL.LAN_LAN_ID = LAN.LAN_ID)
  JOIN SOFTWARE_DEVELOPMENT_CYCLE SDC 
    ON (SDC.SOF_LAN_SOF_LAN_ID = SL.SOF_LAN_ID)
 WHERE SDC.SOF_DC_ID IN (SELECT MAX(SDC2.SOF_DC_ID)
                           FROM SOFTWARE_DEVELOPMENT_CYCLE SDC2
                          WHERE SDC2.SOF_LAN_SOF_LAN_ID = SL.SOF_LAN_ID)
 ORDER BY SOF.VENDOR, 
          SOF.NAME, 
          LAN.LANGUAGE, 
          SOF.VERSION;

Answer 1

You could do something like this to avoid having to hit the SOFTWARE_DEVELOPMENT_CYCLE table a second time

SELECT vendor,
       name,
       language,
       version,
       status,
       sof_dc_id
  FROM (SELECT SOF.VENDOR, 
               SOF.NAME, 
               LAN.LANGUAGE, 
               SOF.VERSION, 
               SDC.STATUS, 
               SDC.SOF_DC_ID,
               RANK() OVER (PARTITION BY sl.sdf_lan_id 
                                ORDER BY sdc.sdf_dc_id DESC) rnk
          FROM SOFTWARE SOF
          JOIN SOFTWARE_LANGUAGES SL 
            ON (SL.SOF_SOF_ID = SOF.SOF_ID)
          JOIN LANGUAGES LAN 
            ON (SL.LAN_LAN_ID = LAN.LAN_ID)
          JOIN SOFTWARE_DEVELOPMENT_CYCLE SDC 
            ON (SDC.SOF_LAN_SOF_LAN_ID = SL.SOF_LAN_ID))
 WHERE rnk = 1
 ORDER BY VENDOR, 
          NAME, 
          LANGUAGE, 
          VERSION;

The RANK analytic function is partitioning the result set by sl.sdf_lan_id. Then for each distinct sl.sdf_lan_id, it is assigning a numeric rank to the row based on the descending order of sdc.sdf_dc_id. That means that the row with the largest sdc.sdf_dc_id for a particular sl.sdf_lan_id will have a RANK of 1. The outer WHERE rnk=1 predicate then selects only the rows that have that maximum value. That should accomplish the same thing that your MAX subquery is accomplishing.