Using nested queries vs CTEs and performance impact - sql

Question

I've been using sql for a while, and would like to know whether and how it would make sense to convert a script containing a lot of CTE's into a regular nested script. I'm using:
WITH cte_account_pricelevelid
AS (SELECT a.accountid,
a.pricelevelid
FROM companypricelist a
JOIN(SELECT accountid
FROM crm_accountbase
WHERE defaultpricelevelid IS NULL) b
ON a.accountid = b.accountid),
totals
AS (SELECT a.accountid,
a.pricelevelid
FROM companypricelist a
JOIN(SELECT accountid
FROM crm_accountbase
WHERE defaultpricelevelid IS NULL) b
ON a.accountid = b.accountid),
totalsgrouped
AS (SELECT pricelevelid,
Count(*) counts
FROM totals
GROUP BY pricelevelid),
final
AS (SELECT cte.accountid,
cte.pricelevelid,
frequency.counts
FROM cte_account_pricelevelid cte
CROSS JOIN totalsgrouped frequency
WHERE cte.pricelevelid = frequency.pricelevelid),
mycolumns
AS (SELECT b.accountid,
b.pricelevelid,
b.counts
FROM (SELECT accountid
FROM crm_accountbase
WHERE defaultpricelevelid IS NULL) a
JOIN final b
ON a.accountid = b.accountid),
e
AS (SELECT *,
Row_number()
OVER (
partition BY accountid
ORDER BY counts, pricelevelid ) AS Recency
FROM mycolumns),
cte_result
AS (SELECT accountid,
pricelevelid
FROM e
WHERE recency = 1)
SELECT a.accountid,
a.defaultpricelevelid,
b.pricelevelid
FROM crm_accountbase a
JOIN cte_result b
ON a.accountid = b.accountid
I feel that it is silly to keep running the same query within my CTE's:
SELECT accountid
FROM crm_accountbase
WHERE defaultpricelevelid IS NULL
But I don't know how to get around it. I suppose that I can convert this into, but don't know if there would be any performance gain.
select * from (select * from(select * from(...
Is there an opportunity to tremendously improve performance by converting this into a nested SQL or just simplifying the CTE? If so, would you kindly get me started?

Answer 1

If accountid is indexed this join will not use that index
The derived table has not index
SELECT a.accountid, a.pricelevelid
FROM companypricelist a
JOIN (SELECT accountid
FROM crm_accountbase
WHERE defaultpricelevelid IS NULL) b
ON a.accountid = b.accountid
This will use an index on accountid
Even if there is not an index on accountid it will be faster
SELECT a.accountid, a.pricelevelid
FROM companypricelist a
JOIN crm_accountbase b
ON a.accountid = b.accountid
AND b.defaultpricelevelid IS NULL

Answer 2

I tried to simplify it a bit. Mind running it and letting me know the results?
WITH
totals
AS (SELECT a.accountid,
a.pricelevelid
FROM companypricelist a
JOIN(SELECT accountid
FROM crm_accountbase
WHERE defaultpricelevelid IS NULL) b
ON a.accountid = b.accountid),
totalsgrouped
AS (SELECT pricelevelid,
Count(*) counts
FROM totals
GROUP BY pricelevelid),
final
AS (SELECT cte.accountid,
cte.pricelevelid,
frequency.counts
FROM totals cte
CROSS JOIN totalsgrouped frequency
WHERE cte.pricelevelid = frequency.pricelevelid),
mycolumns
AS (SELECT b.accountid,
b.pricelevelid,
b.counts
FROM final b
JOIN totals a
ON a.accountid = b.accountid),
e
AS (SELECT *,
Row_number()
OVER (
partition BY accountid
ORDER BY counts, pricelevelid ) AS Recency
FROM mycolumns)
SELECT a.accountid,
a.defaultpricelevelid,
b.pricelevelid
FROM crm_accountbase a
JOIN e b
ON a.accountid = b.accountid
WHERE b.recency = 1