Question

It is bothering me that for a simple query, I have to write out so many sub-selects and WITH statements.

The question is: are there basic guidelines on how to simplify queries that have subqueries?

Here’s my query:

WITH cte_min
     AS (SELECT a.client_id,
                a.specimen_source,
                a.received_date
         FROM   f_accession_daily a
                JOIN (SELECT DISTINCT f.client_id,
                                      f.received_date,
                                      f.accession_daily_key
                      FROM   F_ACCESSION_DAILY f
                             JOIN (SELECT CLIENT_ID,
                                          Min(received_date) MinRecDate
                                   FROM   F_ACCESSION_DAILY
                                   GROUP  BY CLIENT_ID) i
                               ON f.CLIENT_ID = i.CLIENT_ID
                                  AND f.RECEIVED_DATE = i.MinRecDate) b
                  ON a.ACCESSION_DAILY_KEY = b.ACCESSION_DAILY_KEY),
     cte_max
     AS (SELECT a.client_id,
                a.specimen_source,
                a.received_date
         FROM   f_accession_daily a
                JOIN (SELECT DISTINCT f.client_id,
                                      f.received_date,
                                      f.accession_daily_key
                      FROM   F_ACCESSION_DAILY f
                             JOIN (SELECT CLIENT_ID,
                                          Max(received_date) MaxRecDate
                                   FROM   F_ACCESSION_DAILY
                                   GROUP  BY CLIENT_ID) i
                               ON f.CLIENT_ID = i.CLIENT_ID
                                  AND f.RECEIVED_DATE = i.MaxRecDate) b
                  ON a.ACCESSION_DAILY_KEY = b.ACCESSION_DAILY_KEY),
     cte_est
     AS (SELECT DISTINCT client_id,
                         MLIS_DATE_ESTABLISHED
         FROM   D_CLIENT
         WHERE  REC_ACTIVE_FLG = 1
                AND MLIS_DATE_ESTABLISHED IS NOT NULL)
SELECT DISTINCT f.client_id,
                cmin.specimen_source,
                cmin.received_date,
                cmax.specimen_source,
                cmax.received_date,
                cest.MLIS_DATE_ESTABLISHED
FROM   F_ACCESSION_DAILY f
       LEFT JOIN cte_max cmax
         ON cmax.CLIENT_ID = f.CLIENT_ID
       LEFT JOIN cte_min cmin
         ON cmin.CLIENT_ID = f.CLIENT_ID
       LEFT JOIN cte_est cest
         ON cest.CLIENT_ID = f.CLIENT_ID 

I am not asking necessarily for you to do the simplification yourself (although I would be very grateful for this), rather I am asking for general guidelines/directions on re-writing this query to be more elegant.

Answer 1

Does this look any better?

;WITH minmax AS (
SELECT client_id, specimen_source, received_date,
       RMin = row_number() over (partition by Client_id
                                 order by received_date, accession_daily_key),
       RMax = row_number() over (partition by Client_id
                                 order by received_date desc, accession_daily_key desc)
FROM F_ACCESSION_DAILY
)
SELECT f.client_id,
       max(case when rmin=1 then f.specimen_source end),
       max(case when rmin=1 then f.received_date end),
       max(case when rmax=1 then f.specimen_source end),
       max(case when rmax=1 then f.received_date end),
       D.MLIS_DATE_ESTABLISHED
FROM   minmax f
LEFT JOIN D_CLIENT D ON D.REC_ACTIVE_FLG = 1 AND D.MLIS_DATE_ESTABLISHED IS NOT NULL
WHERE 1 in (f.rmin, f.rmax)
GROUP BY f.client_id, D.MLIS_DATE_ESTABLISHED