Question

I have a complex SQL problem in MS SQL Server, and in drawing on a piece of paper I realized that I could think of it as a single bar filled with rectangles, each rectangle having segments with different Z orders. In reality it has nothing to do with z order or graphics at all, but more to do with some complex business rules that would be difficult to explain. Howoever, if anyone has ideas on how to solve the below that will give me my solution.

I have the following data:

ObjectID  |  PercentOfBar  |  ZOrder (where smaller is closer)
---------------------------------------------------------------
A         |  100           |  6
B         |  50            |  5
B         |  50            |  4
C         |  30            |  3
C         |  70            |  6

The result of my query that I want is this, in any order:

PercentOfBar  |  ZOrder
-------------------------
50            |  5
20            |  4
30            |  3

Think of it like this, if I drew rectangle A, it would fill 100% of the bar and have a z order of 6.

6666666666
AAAAAAAAAA

If I then layed out rectangle B, consisting of two segments, both segments would cover up rectangle A resulting in the following rendering:

4444455555
BBBBBBBBBB

As a rule of thumb, for a given rectangle, it’s segments should be layed out such that the highest z order is to the right of the lower Z orders.

Finally rectangle C would cover up only portions of Rectangle B with it’s 30% segment that is z order 3, which would be on the left. You can hopefully see how the is represented in the output dataset I listed above:

3334455555
CCCBBBBBBB

Now to make things more complicated I actually have a 4th column such that this grouping occurs for each key:

Input:

SomeKey, ObjectID, PercentOfBar, ZOrder (where smaller is closer)
X, A, 100, 6
X, B, 50, 5
X, B, 50, 4
X, C, 30, 3
X, C, 70, 6
Y, A, 100, 6
Z, B, 50, 2
Z, B, 50, 6
Z, C, 100, 5

Output:

SomeKey, PercentOfBar, ZOrder
X, 50, 5
X, 20, 4
X, 30, 3
Y, 100, 6
Z, 50, 2
Z, 50, 5

Notice in the output, the PercentOfBar for each SomeKey would add up to 100%.

This is one I know I’m going to be thinking about when I go to bed tonight.

Just to be explicit and have a question:

What would be a query that would produce the results described above?

Answer 1

I’m making the following assumptions:

• You’re using SQL Server 2005 or newer.
• SomeKey, ObjectID, ZOrder is unique.

Other notes:

• I have not optimized the query – I just tried to get the correct result.
• I’ve only tested it on your test data.

With that in mind you could try something like this:

WITH Bars AS (
    SELECT
        T1.SomeKey,
        T1.ObjectID,
        T1.ZOrder,
        SUM(T2.PercentOfBar) - T1.PercentOfBar AS PercentStart,
        SUM(T2.PercentOfBar) AS PercentEnd
    FROM Table1 T1
    JOIN Table1 T2
    ON T1.SomeKey = T2.SomeKey
        AND T1.ObjectID = T2.ObjectID
        AND T1.ZOrder >= T2.ZOrder
    GROUP BY T1.SomeKey, T1.ObjectID, T1.PercentOfBar, T1.ZOrder),
Boundaries AS (
    SELECT P, ROW_NUMBER() OVER (ORDER BY P) AS rn
    FROM (
        SELECT DISTINCT PercentStart AS P FROM Bars
        UNION
        SELECT DISTINCT PercentEnd FROM Bars
    ) T1),
Intervals AS (
    SELECT B1.P AS PercentStart, B2.P AS PercentEnd
    FROM Boundaries B1
    JOIN Boundaries B2
        ON B1.rn + 1 = B2.rn),
Bits AS (
    SELECT
        SomeKey,
        ObjectId,
        ZOrder,
        Intervals.PercentStart,
        Intervals.PercentEnd
    FROM Intervals
    JOIN Bars
        ON Bars.PercentStart <= Intervals.PercentStart
        AND Bars.PercentEnd >= Intervals.PercentEnd),
LowestZOrder AS (
    SELECT SomeKey, PercentStart, MIN(ZOrder) AS ZOrder
    FROM Bits
    GROUP BY SomeKey, PercentStart),
LowestBits AS (
    SELECT Bits.*
    FROM Bits
    JOIN LowestZOrder
        ON Bits.SomeKey = LowestZOrder.SomeKey
        AND Bits.PercentStart = LowestZOrder.PercentStart
        AND Bits.ZOrder = LowestZOrder.ZOrder)
SELECT
    SomeKey,
    MAX(PercentEnd) - MIN(PercentStart) AS PercentOfBar,
    ZOrder
FROM LowestBits
GROUP BY SomeKey, ObjectID, ZOrder
ORDER BY SomeKey, ObjectID, MIN(PercentStart) DESC

Result:

SomeKey PercentOfBar ZOrder
X       50           5
X       20           4
X       30           3
Y       100          6
Z       50           2
Z       50           5

Test data:

CREATE TABLE Table1 (SomeKey NVARCHAR(100) NOT NULL, ObjectID NVARCHAR(100) NOT NULL, PercentOfBar INT NOT NULL, ZOrder INT NOT NULL);
INSERT INTO Table1 (SomeKey, ObjectID, PercentOfBar, ZOrder) VALUES
('X', 'A', 100, 6),
('X', 'B', 50, 5),
('X', 'B', 50, 4),
('X', 'C', 30, 3),
('X', 'C', 70, 6),
('Y', 'A', 100, 6),
('Z', 'B', 50, 2),
('Z', 'B', 50, 6),
('Z', 'C', 100, 5);