If I understood it correctly, you want groups of 63 rows supposing they are consecutives and then select the first row for each group.

WITH T AS (

SELECT

ID,

PeriodBegin,

PeriodEnd,

ROW_NUMBER() OVER(PARTITION BY ID, ((PeriodBegin - 1) / 63) + 1 ORDER BY PeriodBegin) AS rn

FROM

#Intervals

)

SELECT

ID,

PeriodBegin,

PeriodEnd

FROM

T

WHERE

rn = 1

ORDER BY

ID,

PeriodBegin;

GO

This expression ((PeriodBegin - 1) / 63) + 1 assign an incremental group number (63 rows each group) and the ROW_NUMBER enumerate the rows partition by (ID, grpnum). The rest is to select all rows where rn = 1.

I am afraid I am taking it too simple.