How to merge ranges from different tables - sql

Question

Giving the following 2 tables:
T1
------------------
From | To | Value
------------------
10 | 20 | XXX
20 | 30 | YYY
30 | 40 | ZZZ
T2
------------------
From | To | Value
------------------
10 | 15 | AAA
15 | 19 | BBB
19 | 39 | CCC
39 | 40 | DDD
What is the best way to get the result below, using T-SQL on SQL Server 2008?
The From/To ranges are sequential (there are no gaps) and the next From always has the same value as the previous To
Desired result
-------------------------------
From | To | Value1 | Value2
-------------------------------
10 | 15 | XXX | AAA
15 | 19 | XXX | BBB
19 | 20 | XXX | CCC
20 | 30 | YYY | CCC
30 | 39 | ZZZ | CCC
39 | 40 | ZZZ | DDD

Answer 1

First I declare data that looks like the data you posted. Please correct me if any assumptions I have made are wrong. Better would be to post your own declaration in the question so we are all working with the same data.
DECLARE #T1 TABLE (
[From] INT,
[To] INT,
[Value] CHAR(3)
);
INSERT INTO #T1 (
[From],
[To],
[Value]
)
VALUES
(10, 20, 'XXX'),
(20, 30, 'YYY'),
(30, 40, 'ZZZ');
DECLARE #T2 TABLE (
[From] INT,
[To] INT,
[Value] CHAR(3)
);
INSERT INTO #T2 (
[From],
[To],
[Value]
)
VALUES
(10, 15, 'AAA'),
(15, 19, 'BBB'),
(19, 39, 'CCC'),
(39, 40, 'DDD');
Here is my select query to generate your expected result:
SELECT
CASE
WHEN [#T1].[From] > [#T2].[From]
THEN [#T1].[From]
ELSE [#T2].[From]
END AS [From],
CASE
WHEN [#T1].[To] < [#T2].[To]
THEN [#T1].[To]
ELSE [#T2].[To]
END AS [To],
[#T1].[Value],
[#T2].[Value]
FROM #T1
INNER JOIN #T2 ON
(
[#T1].[From] <= [#T2].[From] AND
[#T1].[To] > [#T2].[From]
) OR
(
[#T2].[From] <= [#T1].[From] AND
[#T2].[To] > [#T1].[From]
);

Answer 2

Stealing #isme's data setup, I wrote the following:
;With EPs as (
select [From] as EP from #T1
union
select [To] from #T1
union
select [From] from #T2
union
select [To] from #T2
), OrderedEndpoints as (
select EP,ROW_NUMBER() OVER (ORDER BY EP) as rn from EPs
)
select
oe1.EP,
oe2.EP,
t1.Value,
t2.Value
from
OrderedEndpoints oe1
inner join
OrderedEndpoints oe2
on
oe1.rn = oe2.rn - 1
inner join
#T1 t1
on
oe1.EP < t1.[To] and
oe2.EP > t1.[From]
inner join
#T2 t2
on
oe1.EP < t2.[To] and
oe2.EP > t2.[From]
That is, you create a set containing all of the possible end points of periods (EPs), then you "sort" those and assign each one a row number (OrderedEPs).
Then the final query assembles each "adjacent" pair of rows together, and joins back to the original tables to find which rows from each one overlap the selected range.

Answer 3

The below query finds the smallest ranges, then picks the values back out the tables again:
SELECT ranges.from, ranges.to, T1.Value, T2.Value
FROM (SELECT all_from.from, min(all_to.to) as to
FROM (SELECT T1.FROM
FROM T1
UNION
SELECT T2.FROM
FROM T2) all_from
JOIN (SELECT T1.TO
FROM T1
UNION
SELECT T2.FROM
FROM T2) all_to ON all_from.from < all_to.to
GROUP BY all_from.from) ranges
JOIN T1 ON ranges.from >= T1.from AND ranges.to <= T1.to
JOIN T2 ON ranges.from >= T2.from AND ranges.to <= T2.to
ORDER BY ranges.from

Answer 4

Thanks for the answers, but I ended using a CTE, wgich I think is cleaner.
DECLARE #T1 TABLE ([From] INT, [To] INT, [Value] CHAR(3));
DECLARE #T2 TABLE ([From] INT, [To] INT, [Value] CHAR(3));
INSERT INTO #T1 ( [From], [To], [Value]) VALUES (10, 20, 'XXX'), (20, 30, 'YYY'), (30, 40, 'ZZZ');
INSERT INTO #T2 ( [From], [To], [Value]) VALUES (10, 15, 'AAA'), (15, 19, 'BBB'), (19, 39, 'CCC'), (39, 40, 'DDD');
;with merged1 as
(
select
t1.[From] as from1,
t1.[to] as to1,
t1.Value as Value1,
t2.[From] as from2,
t2.[to] as to2,
t2.Value as Value2
from #t1 t1
inner join #T2 t2
on t1.[From] < t2.[To]
and t1.[To] >= t2.[From]
)
,merged2 as
(
select
case when from2>=from1 then from2 else from1 end as [From]
,case when to2<=to1 then to2 else to1 end as [To]
,value1
,value2
from merged1
)
select * from merged2