Question

I have quite simple problem in SQL Server:

User can have 12 items that are represented in table with ID and Slot (slot is 0-11). When an item is picked up, it should be placed into the lowest empty slot.

I am using following script but it returns first empty slot after the first used slot:

SELECT coalesce ((SELECT MIN(Slot) + 1 FROM Items N1 WHERE N1.name = 'abc'
AND NOT EXISTS(SELECT * FROM Items N2 WHERE N2.name = 'abc'
AND N2.Slot = N1.Slot + 1) AND Slot<11),0)

I would need the script to find lowest slot that does not exist yet. Hope it makes sense 🙂

An example – if the table contains following records, it does not work, returns 5 (should return 0):

ID  Slot Name
10    3  abc
11    4  abc

With this data, it does return 2 correctly.

ID  Slot Name
10    0  abc
11    1  abc

The script should return 1 as this is the first not used number (Slot) lower than 11.

Answer 1

  SELECT coalesce (
                    (SELECT MIN(N1.Slot) + 1 
                       FROM Items N1
                            LEFT OUTER JOIN Items N2 ON N1.Slot+1 = N2.Slot
                      WHERE N1.name = 'abc'
                        AND N2.Slot IS NULL
                        AND N1.Slot < 11)
                   ,0)