Question

Here is my table

Events
Start : Datetime
End : Datetime

I’m trying to make sure that a new Event does not overlap any previously entered events. I’ll admit my SQL knowledge is novice at best. The following is a select statement that gets me close but I can’t figure out how to turn it into a constraint (would I use check?)

SELECT e.*
FROM Events
WHERE Start BETWEEN e.START and e.END
OR End BETWEEN new.START and new.END
OR (Start < e.Start and End > e.End)

I’d imagine if something like that returned anything at all there’s overlap.

Edit: updated “sql” statement to cover for a logical failure on my part. It’s most likely still poorly formed. I really appreciate all of the help!

Answer 1

This would actually have to go into code or a trigger. A constraint operates at the row level only

CREATE TRIGGER TRG_Events_INSERT On EventsFOR INSERT
AS
IF EXISTS (SELECT *
    FROM Events E
        JOIN
        INSERTED INS
         ON
           (E.Start Between INS.START and INS.END)
          OR
           (E.End Between INS.START and INS.END)
          OR
           (E.Start < INS.START and E.End > INS.END)

     WHERE
        E.Key <> INS.Key --already inserted at this point

BEGIN
   ROLLBACK TRAN
   --etc
END
GO