simplifying query that has multiple WITH and multiple subqueries - sql

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

Answer 2

50 rows reporting 5 values and in all of that only two tables are referenced.
In the first CTE you have 4 joins (or virtual joins) to the same table and no other table involved reporting 3 columns. Don't know the key so cannot conclude it can be reduced.
If a cte is not reference more than once then it does not result in less lines of code.
For one this cte can be replaced with less code.
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)
...
cest.MLIS_DATE_ESTABLISHED
...
LEFT JOIN cte_est cest
ON cest.CLIENT_ID = f.CLIENT_ID
reduces to
D_CLIENT.MLIS_DATE_ESTABLISHED
...
LEFT JOIN D_CLIENT
ON D_CLIENT.CLIENT_ID = f.CLIENT_ID
AND D_CLIENT.REC_ACTIVE_FLG = 1
AND D_CLIENT.MLIS_DATE_ESTABLISHED IS NOT NULL

Answer 3

While I am not sure if everyone would consider this simpler and/or easier to read, this is how I would do it:
WITH
cte_MaxMinRecvd As
(
SELECT CLIENT_ID,
Min(received_date) MinRecDate,
Max(received_date) MaxRecDate
FROM F_ACCESSION_DAILY
GROUP BY CLIENT_ID
)
, cte_MaxMinDaily As
(
SELECT *
FROM F_ACCESSION_DAILY f
JOIN cte_MaxMinRecvd i ON f.CLIENT_ID = i.CLIENT_ID
)
, cte_min AS
(
SELECT a.client_id,
a.specimen_source,
a.received_date
FROM F_ACCESSION_DAILY a
WHERE EXISTS(
SELECT *
FROM cte_MaxMinDaily f
WHERE f.RECEIVED_DATE = f.MinRecDate
AND a.ACCESSION_DAILY_KEY = f.ACCESSION_DAILY_KEY
)
)
, cte_max AS
(
SELECT a.client_id,
a.specimen_source,
a.received_date
FROM f_accession_daily a
WHERE EXISTS(
SELECT *
FROM cte_MaxMinDaily f
WHERE f.RECEIVED_DATE = f.MinRecDate
AND a.ACCESSION_DAILY_KEY = f.ACCESSION_DAILY_KEY
)
)
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 D_CLIENT cest ON cest.CLIENT_ID = f.CLIENT_ID
AND cest.REC_ACTIVE_FLG = 1
AND cest.MLIS_DATE_ESTABLISHED IS NOT NULL
Mainly what I did was to
Turn most of the subqueries into CTEs, where applicable,
Merge the Min and Max subqueries together, and
Change the DISTINCT subqueries into EXISTS subqueries, which can be simpler (and usually perform better)
Ooops, I also got rid of the cte_est CTE as Blam suggested..