How to get the MAX() while NOT grouping all columns in SQL Server - sql

Question

I have this query.
The INNER SELECT brings back multiple records. The outer does a SUM & MAX so I only have 1 record:
SELECT z.EmployeeId,
SUM(z.PayrollGap) AS PayrollGap,
MAX(z.PayrollGap) AS PayrollGapMax
FROM (SELECT DISTINCT
a.EmployeeId,
a.PayPeriodStart,
a.PayPeriodEnd,
b.PayPeriodStart AS NextStartDate,
CASE WHEN DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1 < 0 THEN 0
ELSE DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1
END AS PayrollGap
FROM EmployeePayroll a
LEFT JOIN EmployeePayroll b
ON b.EmployeeId = a.EmployeeId
AND b.rn = a.rn + 1
WHERE b.PayPeriodStart IS NOT NULL) z
GROUP BY z.EmployeeId
Along with the MAX(z.PayrollGap), I need to grab the PayPeriodStart as well.
The problem is that if I add the column PayPeriodStart to the query, it'll bring back more than 1 record and I need to do a MAX(z.PayrollGap).
How do I go about running this query but at the same time bringing back the PayPeriodStart RELATED TO MAX(z.PayrollGap)?

Answer 1

Try to split query:
;with cte as
(
SELECT DISTINCT
a.EmployeeId,
a.PayPeriodStart,
a.PayPeriodEnd,
b.PayPeriodStart AS NextStartDate,
CASE WHEN DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1 < 0 THEN 0
ELSE DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1
END AS PayrollGap
FROM EmployeePayroll a
LEFT JOIN EmployeePayroll b
ON b.EmployeeId = a.EmployeeId
AND b.rn = a.rn + 1
WHERE b.PayPeriodStart IS NOT NULL
),
res as
(
SELECT z.EmployeeId,
SUM(z.PayrollGap) AS PayrollGap,
MAX(z.PayrollGap) AS PayrollGapMax
FROM cte z
GROUP BY z.EmployeeId
)
select r.EmployeeId, r.PayrollGap, r.PayrollGapMax, c.PayPeriodStart
from res r
join cte c on c.EmployeeId = r.EmployeeId
and c.PayrollGap = r.PayrollGapMax

Answer 2

If I understand the question correctly you need to join your result set back to EmployeePayroll to add in PayPeriodStart.
Something like:
WITH cte AS (
SELECT DISTINCT
a.EmployeeId,
a.PayPeriodStart,
a.PayPeriodEnd,
b.PayPeriodStart AS NextStartDate,
CASE WHEN DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1 < 0 THEN 0
ELSE DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1
END AS PayrollGap
FROM EmployeePayroll a
LEFT JOIN EmployeePayroll b
ON b.EmployeeId = a.EmployeeId
AND b.rn = a.rn + 1
WHERE b.PayPeriodStart IS NOT NULL
)
SELECT EmployeeId
,PayrollGap
,PayrollGapMax
,PayPeriodStart
FROM (SELECT z.EmployeeId,
SUM(z.PayrollGap) AS PayrollGap,
MAX(z.PayrollGap) AS PayrollGapMax
FROM cte z
GROUP BY z.EmployeeId) x
INNER JOIN
cte ON cte.EmployeeId = x.EmployeeId
AND cte.PayrollGap = x.PayrollGapMax
Which isn't optimized.
Or tested, since no sample data.
Or formatted particularly nicely.

Answer 3

Try:
select distinct A.EmployeeId, A.PayrollGap, A.PayrollGapMax, B.PayPeriodStart
(SELECT z.EmployeeId,
SUM(z.PayrollGap) AS PayrollGap,
MAX(z.PayrollGap) AS PayrollGapMax
FROM (SELECT DISTINCT
a.EmployeeId,
a.PayPeriodStart,
a.PayPeriodEnd,
b.PayPeriodStart AS NextStartDate,
CASE WHEN DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1 < 0 THEN 0
ELSE DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1
END AS PayrollGap
FROM EmployeePayroll a
LEFT JOIN EmployeePayroll b
ON b.EmployeeId = a.EmployeeId
AND b.rn = a.rn + 1
WHERE b.PayPeriodStart IS NOT NULL) z
GROUP BY z.EmployeeId) A
inner join
(SELECT DISTINCT
a.EmployeeId,
a.PayPeriodStart,
a.PayPeriodEnd,
b.PayPeriodStart AS NextStartDate,
CASE WHEN DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1 < 0 THEN 0
ELSE DATEDIFF(d, a.PayPeriodEnd, b.PayPeriodStart) - 1
END AS PayrollGap
FROM EmployeePayroll a
LEFT JOIN EmployeePayroll b
ON b.EmployeeId = a.EmployeeId
AND b.rn = a.rn + 1
WHERE b.PayPeriodStart IS NOT NULL) B
ON A.EmployeeId=B.EmployeeId and B.PayrollGap=A.PayrollGapMax