SQL not efficient enough, tuning assistance required - sql

Question

We have some SQL that is ok on smaller data volumes but poor once we scale up to selecting from larger volumes. Is there a faster alternative style to achieve the same output as below? The idea is to pull back a single unique row to get latest version of the data... The SQL does reference another view but this view runs very fast - so we expect the issue is here below and want to try a different approach
SELECT *
FROM
(SELECT (select CustomerId from PremiseProviderVersionsToday
where PremiseProviderId = b.PremiseProviderId) as CustomerId,
c.D3001_MeterId, b.CoreSPID, a.EnteredBy,
ROW_NUMBER() OVER (PARTITION BY b.PremiseProviderId
ORDER BY a.effectiveDate DESC) AS rowNumber
FROM PremiseMeterProviderVersions a, PremiseProviders b,
PremiseMeterProviders c
WHERE (a.TransactionDateTimeEnd IS NULL
AND a.PremiseMeterProviderId = c.PremiseMeterProviderId
AND b.PremiseProviderId = c.PremiseProviderId)
) data
WHERE data.rowNumber = 1

Answer 1

As Bilal Ayub stated above, the correlated subquery can result in performance issues. See here for more detail. Below are my suggestions:
Change all to explicit joins (ANSI standard)
Use aliases that are more descriptive than single characters (this is mostly to help readers understand what each table does)
Convert data subquery to a temp table or cte (temp tables and ctes usually perform better than subqueries)
Note: normally, you should explicitly create and insert into your temp table but I chose not to do that here as I do not know the data types of your columns.
SELECT d.CustomerId
, c.D3001_MeterId
, b.CoreSPID
, a.EnteredBy
, rowNumber = ROW_NUMBER() OVER(PARTITION BY b.PremiseProviderId ORDER BY a.effectiveDate DESC)
INTO #tmp_RowNum
FROM PremiseMeterProviderVersions a
JOIN PremiseMeterProviders c ON c.PremiseMeterProviderId = a.PremiseMeterProviderId
JOIN PremiseProviders b ON b.PremiseProviderId = c.PremiseProviderId
JOIN PremiseProviderVersionsToday d ON d.PremiseProviderId = b.PremiseProviderId
WHERE a.TransactionDateTimeEnd IS NULL
SELECT *
FROM #tmp_RowNum
WHERE rowNumber = 1

Answer 2

You are running a correlated query that will run in loop, if size of table is small it will be faster, i would suggest to change it and try to join the table in order to get customerid.
(select CustomerId from PremiseProviderVersionsToday where PremiseProviderId = b.PremiseProviderId) as CustomerId

Answer 3

Consider derived tables including an aggregate query that calculates maximum EffectoveDate by PremiseProviderId and unit level query, each using explicit joins (current ANSI SQL standard) and not implicit as you currently use:
SELECT data.*
FROM
(SELECT t.CustomerId, c.D3001_MeterId, b.CoreSPID, a.EnteredBy,
b.PremiseProviderId, a.EffectiveDate
FROM PremiseMeterProviders c
INNER JOIN PremiseMeterProviderVersions a
ON a.PremiseMeterProviderId = c.PremiseMeterProviderId
AND a.TransactionDateTimeEnd IS NULL
INNER JOIN PremiseProviders b
ON b.PremiseProviderId = c.PremiseProviderId
INNER JOIN PremiseProviderVersionsToday t
ON t.PremiseProviderId = b.PremiseProviderId
) data
INNER JOIN
(SELECT b.PremiseProviderId, MAX(a.EffectiveDate) As MaxEffDate
FROM PremiseMeterProviders c
INNER JOIN PremiseMeterProviderVersions a
ON a.PremiseMeterProviderId = c.PremiseMeterProviderId
AND a.TransactionDateTimeEnd IS NULL
INNER JOIN PremiseProviders b
ON b.PremiseProviderId = c.PremiseProviderId
GROUP BY b.PremiseProviderId
) agg
ON data.PremiseProviderId = agg.PremiseProviderId
AND data.EffectiveDate = agg.MaxEffDate