Question

I have 2 SQL Server tables with the following structure

Turns-time

cod_turn (PrimaryKey) 
time     (datetime)

Taken turns

cod_taken_turn (Primary Key)
cod_turn
...

and several other fields which are irrelevant to the problem. I cant alter the table structures because the app was made by someone else.

given a numeric variable parameter, which we will assume to be “3” for this example, and a given time, I need to create a query which looking from that time on, it looks the first 3 consecutive records by time which are not marked as “taken”. For example:

For example, for these turns, starting by the time of “8:00” chosen by the user

 8:00 (not taken)
 9:00 (not taken)
10:00 (taken)
11:00 (not taken)
12:00 (not taken)
13:00 (not taken)
14:00 (taken)

The query it would have to list

11:00
12:00
13:00

I cant figure out how to make the query in pure sql, if possible.

Answer 1

WITH Base AS (
SELECT *,
       CASE WHEN EXISTS(
               SELECT * 
               FROM Taken_turns taken 
               WHERE taken.cod_turn = turns.cod_turn) THEN 1 ELSE 0 END AS taken
FROM   [Turns-time] turns)
, RecursiveCTE As (
SELECT TOP 1 cod_turn, [time], taken AS run, 0 AS grp
FROM  Base 
WHERE [time] >= @start_time
ORDER BY [time]
UNION   ALL
SELECT  R.cod_turn, R.[time], R.run, R.grp
FROM    (
        SELECT  T.*,
                CASE WHEN T.taken = 0 THEN 0 ELSE run+1 END AS run,
                CASE WHEN T.taken = 0 THEN grp + 1 ELSE grp END AS grp,
                rn = ROW_NUMBER() OVER (ORDER BY T.[time])
        FROM    Base T
        JOIN    RecursiveCTE R
                ON  R.[time] < T.[time]
        ) R
WHERE   R.rn = 1 AND run < @run_length
),  T AS(
SELECT *, 
        MAX(grp) OVER () AS FinalGroup,
        COUNT(*) OVER (PARTITION BY grp) AS group_size
FROM RecursiveCTE
)
SELECT cod_turn,time
FROM T 
WHERE grp=FinalGroup AND group_size=@run_length