T-SQL query - row iteration without cursor - sql

Question

I have a table
T (variable_name, start_no, end_no)
that holds values like:
(x, 10, 20)
(x, 30, 50)
(x, 60, 70)
(y, 1, 3)
(y, 7, 8)
All intervals are guaranteed to be disjoint.
I want to write a query in T-SQL that computes the intervals where a variable is not searched:
(x, 21, 29)
(x, 51, 59)
(y, 4, 6)
Can I do this without a cursor?
I was thinking of partitioning by variable_name and then ordering by start_no. But how to proceed next? Given the current row in the rowset, how to access the "next" one?

Answer 1

Since you didn't specify which version of SQL Server, I have multiple solutions. If you have are still rocking SQL Server 2005, then Giorgi's uses CROSS APPLY quite nicely.
Note: For both solutions, I use the where clause to filter out improper values so even if the the data is bad and the rows overlap, it will ignore those values.
My Version of Your Table
DECLARE #T TABLE (variable_name CHAR, start_no INT, end_no INT)
INSERT INTO #T
VALUES ('x', 10, 20),
('x', 30, 50),
('x', 60, 70),
('y', 1, 3),
('y', 7, 8);
Solution for SQL Server 2012 and Above
SELECT *
FROM
(
SELECT variable_name,
LAG(end_no,1) OVER (PARTITION BY variable_name ORDER BY start_no) + 1 AS start_range,
start_no - 1 AS end_range
FROM #T
) A
WHERE end_range > start_range
Solution for SQL 2008 and Above
WITH CTE
AS
(
SELECT ROW_NUMBER() OVER (PARTITION BY variable_name ORDER BY start_no) row_num,
*
FROM #T
)
SELECT A.variable_name,
B.end_no + 1 AS start_range,
A.start_no - 1 AS end_range
FROM CTE AS A
INNER JOIN CTE AS B
ON A.variable_name = B.variable_name
AND A.row_num = B.row_num + 1
WHERE A.start_no - 1 /*end_range*/ > B.end_no + 1 /*start_range*/

Answer 2

Here is another version with cross apply:
DECLARE #t TABLE ( v CHAR(1), sn INT, en INT )
INSERT INTO #t
VALUES ( 'x', 10, 20 ),
( 'x', 30, 50 ),
( 'x', 60, 70 ),
( 'y', 1, 3 ),
( 'y', 7, 8 );
SELECT t.v, t.en + 1, c.sn - 1 FROM #t t
CROSS APPLY(SELECT TOP 1 * FROM #t WHERE v = t.v AND sn > t.sn ORDER BY sn)c
WHERE t.en + 1 < c.sn
Fiddle http://sqlfiddle.com/#!3/d6458/3

Answer 3

For each end_no you should find the nearest start_no > end_no then exclude rows without nearest start_no (last rows for the variable_name)
WITH A AS
(
SELECT variable_name, end_no+1 as x1,
(SELECT MIN(start_no)-1 FROM t
WHERE t.variable_name = t1.variable_name
AND t.start_no>t1.end_no) as x2
FROM t as t1 )
SELECT * FROM A WHERE x2 IS NOT NULL
ORDER BY variable_name,x1
SQLFiddle demo
Also here is my old answer to the similar question:
Allen's Interval Algebra operations in SQL

Answer 4

Here's a non-CTE version that seems to work: http://sqlfiddle.com/#!9/4fdb4/1
Given the guaranteed disjoint ranges, I just joined T to itself, computed the next range as the increment/decrement of the adjoining range, then ensuring the new range didn't overlap any existing ranges.
select t1.variable_name, t1.end_no+1, t2.start_no-1
from t t1
join t t2
on t1.variable_name=t2.variable_name
where t1.start_no < t2.start_no
and t1.end_no < t2.end_no
and not exists (select *
from t
where ((t2.start_no-1< t.end_no
and t1.end_no+1 > t.start_no) or
(t1.end_no + 1 < t.end_no and
t2.start_no-1 > t.end_no))
and t.variable_name=t1.variable_name)

Answer 5

This is very portable as it doesn't require CTEs or analytic functions. I could also easily be rewritten without the derived table if that were ever necessary.
select * from (
select
variable_name,
end_no + 1 as start_no,
(
select min(start_no) - 1
from T as t2
where t2.variable_name = t1.variable_name and t2.start_no > t1.end_no
) as end_no
from T as t1
) as intervals
where start_no <= end_no
The number of complemented intervals will be at maximum one fewer than the what you start with. (Some will be eliminated if two ranges were actually consecutive.) So it's easy to take each separate intervals and calculate the one just to its right (or left if you wanted to reverse some of the logic.)