How do I merge 2 rows into 1 row in SQL? - sql

Question

ReportDateTime EuId1 EuId2
2020-02-01 1:00 1576 Null
2020-02-01 1:00 Null 1579
2020-02-01 2:00 Null 1573
2020-02-01 2:00 1566 Null
This is what I have and this is what I want...
ReportDateTime EuId1 EuId2
2020-02-01 1:00 1576 1579
2020-02-01 2:00 1566 1573
Here is my code...
;WITH cteEq AS (
SELECT e.EntHID, e.EntCode, e.EntName
FROM cfEntity fac (NOLOCK)
JOIN cfEntityRelation er (NOLOCK) ON fac.EntHID = er.EntParentHID AND er.EntRelEffEnd = '12/31/2078'
JOIN cfEntity e (NOLOCK) ON er.EntChildHID = e.EntHID AND e.EntTypeTID = -200020
WHERE e.EntHID IN (SELECT ea.EaHID FROM cfEntityAttribute ea (NOLOCK) WHERE ea.EaKey = 'AirPermitXref_Diesel')
)
SELECT
ReportDateTime = a.EqReportDate
, EuId1 = CASE
WHEN EntName LIKE '%EU1%' THEN a.EqPwr
END
, EuId2 = CASE
WHEN EntName LIKE '%EU2%' THEN a.EqPwr
END
FROM eqHourlyAir a (NOLOCK)
JOIN cteEq e (NOLOCK) ON a.EqHID = e.EntHID
OUTER APPLY (
SELECT ad.EqHID, ad.EqReportDate, ad.EqRunTime
FROM eqHourlyAir ad (NOLOCK)
LEFT JOIN cfEntityAttribute ea (NOLOCK) ON ad.EqHID = CAST(ea.EaValue AS INT) AND ea.EaKey = 'AirPermitXref_DWI'
WHERE ea.EaHID = a.EqHID
AND ad.EqReportDate = a.EqReportDate
) dwi
OUTER APPLY (
SELECT ad.EqHID, ad.EqReportDate, ad.EqRunTime
FROM eqHourlyAir ad (NOLOCK)
LEFT JOIN cfEntityAttribute ea (NOLOCK) ON ad.EqHID = CAST(ea.EaValue AS INT) AND ea.EaKey = 'AirPermitXref_Diesel'
WHERE ea.EaHID = a.EqHID
AND ad.EqReportDate = a.EqReportDate
) dsl
WHERE CAST(a.EqReportDate AS DATE) >= #StartDate AND CAST(a.EqReportDate AS DATE) <= #EndDate
ORDER BY a.EqReportDate

Answer 1

using nolock hint is not the best idea !
if you have one null value and only one non value for each reportingdate you can grooup by ReportDateTime and get the max value :
...
SELECT
ReportDateTime = a.EqReportDate,
EuId1 = MAX(CASE WHEN EntName LIKE '%EU1%' THEN a.EqPwr END),
EuId2 = MAX(CASE WHEN EntName LIKE '%EU2%' THEN a.EqPwr END)
FROM
{...}
WHERE
CAST(a.EqReportDate AS DATE) >= #StartDate
AND CAST(a.EqReportDate AS DATE) <= #EndDate
GROUP BY a.EqReportDate
ORDER BY
a.EqReportDate

Answer 2

From you sample data it's very easy to select your desired result as below:
select ReportDateTime ,max(EuId1) EuId1,max(EuId2) EuId2 from
(select * from table1 join table2 on .... )t
group by ReportDateTime
But your query indicates that there is more to the story. Please share some more information.