SQL Group Range Values - sql

Question

I have taken a look at several other questions/answers on here but I cannot apply those to my problem. I am trying to identify multiple sequential breaks based on a key column. Most examples I have found do not deal with multiple breaks in a sequence for the same key column.
Sample data:
Location Number
------------------------
300 15
300 16
300 17
300 18
300 21
300 22
300 23
400 10
400 11
400 14
400 16
Here is the result I am looking for:
Location StartNumber StartNumber
------------------------------------------
300 15 18
300 21 23
400 10 11
400 14 14
400 16 16

Answer 1

Here's as relatively portable SQL solution since you didn't specify the DB
Create Table SampleData (Location int, Number Int)
INSERT INTO SampleData VALUES (300, 15)
INSERT INTO SampleData VALUES (300, 16)
INSERT INTO SampleData VALUES (300, 17)
INSERT INTO SampleData VALUES (300, 18)
INSERT INTO SampleData VALUES (300, 21)
INSERT INTO SampleData VALUES (300, 22)
INSERT INTO SampleData VALUES (300, 23)
INSERT INTO SampleData VALUES (400, 10)
INSERT INTO SampleData VALUES (400, 11)
INSERT INTO SampleData VALUES (400, 14)
INSERT INTO SampleData VALUES (400, 16)
SELECT
t1.Location,
t1.Number AS startofgroup,
MIN(t2.Number) AS endofgroup
FROM (SELECT Number , Location
FROM SampleData tbl1
WHERE NOT EXISTS(SELECT *
FROM SampleData tbl2
WHERE tbl1.Number - tbl2.Number = 1
and tbl1.Location = tbl2.Location)) t1
INNER JOIN (SELECT Number , Location
FROM SampleData tbl1
WHERE NOT EXISTS(SELECT *
FROM SampleData tbl2
WHERE tbl2.Number - tbl1.Number = 1
and tbl1.Location = tbl2.Location)) t2
ON t1.Number <= t2.Number
and t1.Location = t2.Location
GROUP BY
t1.Location,
t1.Number
ORDER BY
Location,
startofgroup
Output
Location startofgroup endofgroup
----------- ------------ -----------
300 15 18
300 21 23
400 10 11
400 14 14
400 16 16
Its a modified version of Listing 2. A set-based solution for identifying islands. From Islands and Gaps in Sequential Numbers by Alexander Kozak
If you're looking for more options with SQL Server 2005 and later you should search for the phrase "Itzik Ben-Gan gaps and islands"

Answer 2

Well, if you're using an RDBMS that supports the lag() function, then this should tell you where the breaks are. You should then be able to use this, along with some case statements and careful use of the min() and max() functions, to get the query that you want.
select location, lag_number as startnumber, number as endnumber
from(select location, number, lag_number
from(
select location, number
, lag(number) over (partition by location order by number) as lag_number
from table
)a
where number is not null and lag_number is not null
)b
where number-lag_number>1 order by 1,2,3;