Subquery Building a Column - sql

Question

I am wondering if there is a more efficient way of doing the following query.
SELECT
t.iCertification_UserCertificationTranscriptID AS I_CERT_TRANSCRIPT_DIM,
t.iHR_UserID AS I_EMP_DIM,
t.iCertification_CertificationID AS I_RUL_CERT_DIM,
(
SELECT iHR_PositionID
FROM UserProfileNoGroups AS prof
WHERE
(iHR_UserID = t.iHR_UserID)
AND (Profile_IsPrimary = '1')
AND (UserPosition_IsPrimary = '1')
AND (t.dEffectiveStart BETWEEN UserPosition_Effective AND COALESCE(UserPosition_End, LOCALTIMESTAMP))
ORDER BY UserPosition_Effective DESC
FETCH FIRST 1 ROWS ONLY
) AS I_POSN_DIM,
CAST(EXTRACT(YEAR FROM t.dEffectiveStart) * 10000 + EXTRACT(MONTH FROM t.dEffectiveStart) * 100 + EXTRACT(DAY FROM t.dEffectiveStart) AS INT) AS I_DAY_STRT_DIM,
CAST(EXTRACT(YEAR FROM t.dEffectiveEnd) * 10000 + EXTRACT(MONTH FROM t.dEffectiveEnd) * 100 + EXTRACT(DAY FROM t.dEffectiveEnd) AS INT) AS I_DAY_END_DIM,
CASE
WHEN t.iCertification_TranscriptSourceID = '1' THEN 'Y'
ELSE 'N'
END AS L_AdminOverride,
t.mComment AS X_Comment
FROM
dbo.tCertification_UCT AS t;
I am concerned of the query that builds column I_POSN_DIM. The query performs slowly and it seems like that query has to be scanned over and over to extract results. This is in postgresql and I am not that familiar with this platform. I tried using CTEs that uses the MAX function, but the COUNT always turns out different from this query. Any assistance would be appreaciated.

Answer 1

I thought something like this:
SELECT
t.iCertification_UserCertificationTranscriptID AS I_CERT_TRANSCRIPT_DIM,
t.iHR_UserID AS I_EMP_DIM,
t.iCertification_CertificationID AS I_RUL_CERT_DIM,
uPG.iHR_PositionID AS I_POSN_DIM,
(t.dEffectiveStart.Year * 10000 + t.dEffectiveStart.Month * 100 + t.dEffectiveStart.Day) AS I_DAY_STRT_DIM,
(t.dEffectiveEnd.Year * 10000 + t.dEffectiveEnd.Month * 100 + t.dEffectiveEnd.Day) AS I_DAY_END_DIM,
CASE WHEN t.iCertification_TranscriptSourceID = '1' THEN 'Y' ELSE 'N' END AS L_AdminOverride,
t.mComment AS X_Comment
FROM dbo.tCertification_UCT AS t
INNER JOIN UserProfileNoGroups uPG ON t.iHR_UserID = uPG.iHR_UserID
WHERE Profile_IsPrimary = '1'
AND UserPosition_IsPrimary = '1'
AND (t.dEffectiveStart BETWEEN UserPosition_Effective AND COALESCE(UserPosition_End, LOCALTIMESTAMP));
I moved the inner query to outside and I convert it in an equivalent inner join. In others fields you did cast but it's not neccesary because of the result from that operations is an int.
But I supossed that table UserProfileNoGroups has 1 record for each record at tCertification_UCT. If it's not this way, the query would change a litlle:
SELECT
t.iCertification_UserCertificationTranscriptID AS I_CERT_TRANSCRIPT_DIM,
t.iHR_UserID AS I_EMP_DIM,
t.iCertification_CertificationID AS I_RUL_CERT_DIM,
uPG.iHR_PositionID OVER (ORDER BY UserPosition_Effective DESC) AS I_POSN_DIM,
(t.dEffectiveStart.Year * 10000 + t.dEffectiveStart.Month * 100 + t.dEffectiveStart.Day) AS I_DAY_STRT_DIM,
(t.dEffectiveEnd.Year * 10000 + t.dEffectiveEnd.Month * 100 + t.dEffectiveEnd.Day) AS I_DAY_END_DIM,
CASE WHEN t.iCertification_TranscriptSourceID = '1' THEN 'Y' ELSE 'N' END AS L_AdminOverride,
t.mComment AS X_Comment
FROM dbo.tCertification_UCT AS t
INNER JOIN UserProfileNoGroups uPG ON t.iHR_UserID = uPG.iHR_UserID
WHERE Profile_IsPrimary = '1'
AND UserPosition_IsPrimary = '1'
AND (t.dEffectiveStart BETWEEN UserPosition_Effective AND COALESCE(UserPosition_End, LOCALTIMESTAMP));
You can play with OVER clause:
https://www.postgresql.org/docs/9.1/tutorial-window.html