SQL query optimization - make only one join on table - sql

Question

I have a large SQL query, where I need to select some data.
SELECT p.Id, p.UserId, u.Name AS CreatedBy, p.JournalId, p.Title, pt.Name AS PublicationType, p.CreatedDate, p.MagazineTitle, /*ps.StatusId,*/ p.Authors, pb.Name AS Publisher, p.Draft,jns.Name AS JournalTitle,
ISNULL(
ISNULL(
(SELECT StatusId FROM [PublicationsStatus] WHERE StatusDate=
(SELECT MAX(StatusDate) FROM [PublicationsStatus] AS ps WHERE ps.PublicationId = p.Id )),--AND ps.UserId = #UserId ORDER BY StatusDate DESC),
(SELECT TOP(1) ActionId + 6 FROM [PublicationsQuoteSaleLines] AS pqsl WHERE pqsl.PublicationId = p.Id ORDER BY pqsl.Id)
),
1
)AS StatusId
,ISNULL(
(SELECT MAX(StatusDate) FROM [PublicationsStatus] AS ps WHERE ps.PublicationId = p.Id ),--AND ps.UserId = #UserId),
p.CreatedDate
) AS StatusDate
,ISNULL(
(cast((SELECT MAX(StatusDate) FROM [PublicationsStatus] AS ps WHERE ps.PublicationId = p.Id) as date) ),--AND ps.UserId = #UserId),
p.CreatedDate
) AS StDate
,CASE
WHEN ISNULL(
ISNULL(
(SELECT StatusId FROM [PublicationsStatus] WHERE StatusDate=
(SELECT MAX(StatusDate) FROM [PublicationsStatus] AS ps WHERE ps.PublicationId = p.Id )),--AND ps.UserId = #UserId ORDER BY StatusDate DESC),
(SELECT TOP(1) ActionId + 6 FROM [PublicationsQuoteSaleLines] AS pqsl WHERE pqsl.PublicationId = p.Id ORDER BY pqsl.Id)
),
1 ) IN (1, 7, 8) THEN 0
ELSE 1 END AS OrderCriteria
,(SELECT COUNT(*) FROM SentEmails AS se WHERE se.PublicationId = p.Id AND se.EmailType = 1 AND se.UserId = #UserId) AS NumberOfAlerts
,(SELECT COUNT(*) FROM SentEmails AS se WHERE se.PublicationId = p.Id AND se.EmailType = 3 AND se.UserId = #UserId) AS NumberOfReminders
FROM Publications AS p
LEFT JOIN PublicationTypes AS pt ON p.PublicationTypeId = pt.Id
LEFT JOIN Publishers AS pb ON p.PublisherId = pb.Id
LEFT JOIN Journals As jns ON p.JournalId = jns.Id
LEFT JOIN Users AS u ON u.Id = p.UserId
The problem is that the query is slow. AS you can see I have the same thing at OrderCriteria and the StatusId. The StatusDate I'm getting from the same table.
I thought that I could resolve the performance to make only one \
LEFT JOIN
something like this:
LEFT JOIN (
SELECT
PublicationId,
StatusId AS StatusId,
StatusDate AS StatusDate
FROM [PublicationsStatus] WHERE StatusDate=
(
SELECT MAX(StatusDate) FROM PublicationsStatus
)
) AS ps ON ps.PublicationId = p.Id
but I did not get the same results this way.
Can you please advise?

Answer 1

I tried to simplify your query using a few CTE to avoid doing the same subquery multiple times. You can try this out and see if it's still slow.
;WITH MaxStatusDateByPublication AS
(
SELECT
PublicationId = ps.PublicationId,
MaxStatusDate = MAX(ps.StatusDate)
FROM
[PublicationsStatus] AS ps
GROUP BY
PS.PublicationId
),
StatusForMaxDateByPublication AS
(
SELECT
StatusId = PS.StatusId,
M.PublicationId,
M.MaxStatusDate
FROM
MaxStatusDateByPublication AS M
INNER JOIN [PublicationsStatus] AS PS ON
M.PublicationId = PS.PublicationId AND
M.MaxStatusDate = PS.StatusDate
),
SentEmailsByPublicationAndType AS
(
SELECT
S.PublicationID,
S.EmailType,
AmountSentEmails = COUNT(1)
FROM
SentEmails AS S
WHERE
S.EmailType IN (1, 3) AND
S.UserID = #UserId
GROUP BY
S.PublicationID,
S.EmailType
)
SELECT
p.Id,
p.UserId,
u.Name AS CreatedBy,
p.JournalId,
p.Title,
pt.Name AS PublicationType,
p.CreatedDate,
p.MagazineTitle,
p.Authors,
pb.Name AS Publisher,
p.Draft,
jns.Name AS JournalTitle,
COALESCE(MS.StatusId, SL.StatusId, 1) AS StatusId,
ISNULL(MS.MaxStatusDate, P.CreatedDate) AS StatusDate,
ISNULL(CONVERT(DATE, MS.MaxStatusDate), P.CreatedDate) AS StDate,
CASE
WHEN COALESCE(MS.StatusId, SL.StatusId, 1) IN (1, 7, 8) THEN 0
ELSE 1
END AS OrderCriteria,
ISNULL(TY1.AmountSentEmails, 0) AS NumberOfAlerts,
ISNULL(TY3.AmountSentEmails, 0) AS NumberOfReminders
FROM
Publications AS p
LEFT JOIN PublicationTypes AS pt ON p.PublicationTypeId = pt.Id
LEFT JOIN Publishers AS pb ON p.PublisherId = pb.Id
LEFT JOIN Journals As jns ON p.JournalId = jns.Id
LEFT JOIN Users AS u ON u.Id = p.UserId
LEFT JOIN StatusForMaxDateByPublication AS MS ON P.Id = MS.PublicationId
LEFT JOIN SentEmailsByPublicationAndType AS TY1 ON
P.Id = TE.PublicationID AND
TY1.EmailType = 1
LEFT JOIN SentEmailsByPublicationAndType AS TY3 ON
P.Id = TE.PublicationID AND
TY1.EmailType = 3
OUTER APPLY (
SELECT TOP 1
StatusId = ActionId + 6
FROM
[PublicationsQuoteSaleLines] AS pqsl
WHERE
pqsl.PublicationId = P.Id
ORDER BY
pqsl.Id ASC) AS SL
Try to avoid writing the same expression several times (and specially if it involes subqueries inside a column!). Using a few CTEs and proper identing will help readability.
This is a complex query and involves several tables. If your query runs slow it might be for many different reasons. Try executing each subquery on it's own to check if they are slow or not, then try joining them 1 by 1. Indexes by the join columns will probably increase your performance if they don't exist already. Posting the full query execution plan might help.