ms sql table adding rows whenever level changes by more than 1 so that every row has difference of 1 in start_level and end_level - sql-server

Question

(This is my first stack overflow question. So please let me know suggestions for posing a better question, if you cannot understand.)
I have a table of around 500 people(users) who are going up the stairs from floor x (0=x, max(y) = 50). A person can climb zero/one or many levels in a single go which corresponds to a single row of the table along with the time taken to do so in seconds.
I want to find average time taken to go from floor a to a+1 where a is any of the floor number. To do so I intend to divide every row of the mentioned table into rows which have start_level+1= end_level. Duration will be divided equally as shown in EXPECTED OUTPUT TABLE for user b.
GIVEN TABLE INPUT
start_level end_level duration user
1 1 10 a
1 2 5 a
2 5 27 b
5 6 3 c
EXPECTED OUTPUT
start_level end_level duration user
1 1 10 a
1 2 5 a
2 3 27/3 b
3 4 27/3 b
4 5 27/3 b
5 6 3 c
Note: level jumps are in integers only.
After getting expected output, I can simply create a column sum(duration)/count(distinct users) at a start_level level to get average time taken to get one floor above from each floor.
Any help is appreciated.

Answer 1

You can use a Numbers table to "create" the incremental steps. Here's my setup:
CREATE TABLE #floors
(
[start_level] INT,
[end_level] INT,
[duration] DECIMAL(10, 4),
[user] VARCHAR(50)
)
INSERT INTO #floors
([start_level],
[end_level],
[duration],
[user])
VALUES (1,1,10,'a'),
(1,2,5,'a'),
(2,5,27,'b'),
(5,6,3,'c')
Then, using a Numbers table and some LEFT JOIN/COALESCE logic:
-- Create a Numbers table
;WITH Numbers_CTE
AS (SELECT TOP 50 [Number] = ROW_NUMBER()
OVER(
ORDER BY (SELECT NULL))
FROM sys.columns)
SELECT [start_level] = COALESCE(n.[Number], f.[start_level]),
[end_level] = COALESCE(n.[Number] + 1, f.[end_level]),
[duration] = CASE
WHEN f.[end_level] = f.[start_level] THEN f.[duration]
ELSE f.[duration] / ( f.[end_level] - f.[start_level] )
END,
f.[user]
FROM #floors f
LEFT JOIN Numbers_CTE n
ON n.[Number] BETWEEN f.[start_level] AND f.[end_level]
AND f.[end_level] - f.[start_level] > 1
Here are the logical steps:
LEFT JOIN the Numbers table for cases where end_level >= start_level + 2 (this has the effect of giving us multiple rows - one for each incremental step)
new start_level = If the LEFT JOIN "completes": take Number from the Numbers table, else: take the original start_level
new end_level = If the LEFT JOIN "completes": take Number + 1, else: take the original end_level
new duration = If end_level = start_level: take the original duration (to avoid divide by 0), else: take the average duration over end_level - start_level