Transact SQL :: Script To Merge Similar Content?

I have a table which contains single legs. E.g.

Row Leg-ID From To On DateFrom DateTo DOW

1 ABC123 AAA BBB CCC 01JAN15 01JAN15 1

2 ABC123 AAA BBB CCC 07JAN15 07JAN15 1

3 ABC123 AAA BBB CCC 14JAN15 14JAN15 1

4 ABC123 XXX YYY ZZZ 21JAN15 21JAN15 1

I now want to merge those single records, which follow a pattern. For the above case this would be Row 1+2+3, so the result should be:

Row Leg-ID
From To
On DateFrom
DateTo DOW
1 ABC123
AAA BBB
CCC 01JAN15
14JAN15 1
3 ABC123
XXX YYY
ZZZ 14JAN15
14JAN15 1

The pattern is, that the legs from Row 1 and 2 have identical attributes (Leg-ID, From, To, On, DOW) and are on consecutive weeks on the same weekday. I was doing this through a while-look:

check if there is a record matching the following week (a.DateTo = dateadd(d, 7, b.DateFrom))if there is a match, then update the previous week record DateTo with the following week DateFromdelete the following week record but this is very slow, for 50T rows it runs approx. 6 hrs to shrink everything..