SQL: insert to unique column with shift - sql

Question

I need to store data with varchar name and Integer intValue. All integer values are unique and I need to keep up that contract
I need to write query to add the element using the following rule: if after insertion there is an intValue duplication - we need to increase intValue of existed element to resolve conflict. Repeat that operation until no conflict left.
Example:
B | 2 | | B | 2 |
C | 3 | | E | 3 |
D | 4 | => insert (E 3) => | C | 4 |
A | 1 | | D | 5 |
Z | 7 | | A | 1 |
| Z | 7 |
The only idea is to run update query in a loop but that looks too unefficient.
I need to write this query in Spring JPA, so the only requirement that the query should not be database specific
Business case:
Let's say there is a people in the queue. And intValue is position in the queue. So, "Add" means that some person come, pay money and say: I dont wanna be the last in the queue. I want to be, for example, the 3rd. So you take the money and put that person in a queue so other people after him - increments their position.
The only difference from the queue - that in my case there are gaps allowed

Answer 1

Aha, we might say that the gaps are occasioned by people leaving the queue.
Lets try this. Loops are inevitable--either server does them, or we can do as SQL.
-- prepare test data
declare #PeopleQueue table (pqname varchar(100), intValue int);
insert into #PeopleQueue
SELECT 'B' AS pqname, 2 as intValue UNION ALL
SELECT 'C' AS pqname, 3 as intValue UNION ALL
SELECT 'D' AS pqname, 4 as intValue UNION ALL
SELECT 'A' AS pqname, 1 as intValue UNION ALL
SELECT 'Z' AS pqname, 7 as intValue
;
--SELECT '' AS pqname, 0 as intValue UNION ALL
Select * from #PeopleQueue; - verify good test data
-- Solve the problem
Declare #pqnameNEW varchar(100) = 'E';
Declare #intNEW int = 3; -- 3 for conflict, or for no conflict, use 13
Declare #intHIGH int;
IF EXISTS ( SELECT 1 FROM #PeopleQueue WHERE intValue = #intNEW )
BEGIN
-- find the end of the sequence, before the gap
SET #intHIGH = (
SELECT TOP 1
intValue
FROM #PeopleQueue pq
WHERE NOT EXISTS
(
SELECT NULL
FROM #PeopleQueue pn
WHERE pn.intValue = pq.intValue + 1
)
AND pq.intValue >= #intNEW
)
;
-- now Update all from intNEW thru intHIGH
UPDATE #PeopleQueue
SET intValue = intValue + 1
WHERE intValue >= #intNEW
AND intValue <= #intHIGH
End;
-- finally insert the new item
INSERT into #PeopleQueue Values (#pqnameNEW, #intNEW);
Select * from #PeopleQueue; -- verify correct solution
Edited--11/28 17:00
Or, estimate the number of Bump-the-Line-Inserts (vs append to the end inserts), and design the intValues to be originally in multiples of ten (10) so that long sequences of updates are minimized.

Answer 2

update queue
SET intValue = intValue + 1
WHERE intValue >= 3
AND intValue <= (
SELECT q1.intValue
FROM queue as q1 LEFT JOIN queue AS q2 ON q1.intValue + 1 = q2.intValue
WHERE q2.name is NULL AND q1.intValue > 3
ORDER BY q1.intValue
LIMIT 1
)