How to merge ranges from different tables

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.