Trigger to update rank dynamically - sql-server-2008-r2

Question

I want to write trigger for insert update and Delete. O have one table named (tbl_rank) which have primary key (ID).
ID Name Rank
1 A 1
2 B 2
3 C 3
4 D 4
5 E 5
Now I want to insert new rank but conditions are
1) if I enter 6 it will be 6
2) if I enter 7 it also should be 6 (I mean in sequence)
3) if I enter 2 than than entered rank will be 2 and 2 will be 3 and so on
For delete trigger
1) if I delete 5 the rank should be 1 to 4
2) if I delete 2 the rank would be rearranged and 3 should be 2 and 4 would be 3 and so on
for update trigger
1) if I update 3 to 5 than 4 would be 3 and 5 would be 4
2) if I update 5 to 3 than 3 would be 4 and 4 would be 5
I wrote insert and delete trigger its working fine but in update I am getting uneven result.

Answer 1

Can you not just have tbl_rank as a view then you don't need any triggers? To rank them in the view you can use a windowed function row_number() over (order by Id)
How is the initial update performed? If you know it is an update then you need to do a delete and insert just for the effected range. Eg changing 3 to 5. You delete records for 3 to 5 then insert those 3 records again with the different ids. An update statement essentially does this anyway

Answer 2

There is an assumption that id is not an auto-identity column.
CREATE TRIGGER trg_tbl_rank
ON tbl_rank
INSTEAD OF INSERT,DELETE,UPDATE
AS
BEGIN
SET NOCOUNT ON;
DECLARE #v_deleted_rank INT;
DECLARE #v_inserted_rank INT;
DECLARE #v_max_rank INT;
SELECT #v_deleted_rank = COALESCE(rank, 0) FROM deleted;
SELECT #v_inserted_rank = COALESCE(rank, 0) FROM inserted;
SELECT #v_max_rank = COALESCE(MAX(rank), 0) FROM tbl_rank;
IF #v_deleted_rank > 0
BEGIN
DELETE FROM tbl_rank
WHERE id = (SELECT id FROM deleted);
UPDATE tbl_rank
SET rank = rank - 1
WHERE rank > #v_deleted_rank;
END
IF #v_inserted_rank > 0
BEGIN
IF #v_inserted_rank <= #v_max_rank
BEGIN
UPDATE tbl_rank
SET rank = rank + 1
WHERE rank >= #v_inserted_rank;
INSERT INTO tbl_rank (id, name, rank)
SELECT id, name, #v_inserted_rank FROM inserted;
END
ELSE
INSERT INTO tbl_rank (id, name, rank)
SELECT id, name, #v_max_rank + 1 FROM inserted;
END
END
GO
Here are queries to test:
INSERT INTO tbl_rank (id, name, rank) VALUES (1, 'A', 1);
INSERT INTO tbl_rank (id, name, rank) VALUES (2, 'B', 2);
INSERT INTO tbl_rank (id, name, rank) VALUES (3, 'C', 3);
INSERT INTO tbl_rank (id, name, rank) VALUES (4, 'D', 4);
INSERT INTO tbl_rank (id, name, rank) VALUES (5, 'E', 5);
SELECT * FROM tbl_rank;
INSERT INTO tbl_rank (id, name, rank) VALUES (6, 'F', 7);
SELECT * FROM tbl_rank;
INSERT INTO tbl_rank (id, name, rank) VALUES (7, 'G', 2);
SELECT * FROM tbl_rank;
DELETE FROM tbl_rank WHERE rank = 7;
SELECT * FROM tbl_rank;
DELETE FROM tbl_rank WHERE rank = 2;
SELECT * FROM tbl_rank;
UPDATE tbl_rank SET rank = 5 WHERE rank = 3;
SELECT * FROM tbl_rank;
UPDATE tbl_rank SET rank = 3 WHERE rank = 5;
SELECT * FROM tbl_rank;
TRUNCATE TABLE tbl_rank;

Answer 3

I want to write trigger for insert update and Delete I have one table named(tbl_rank)which have primary key(ID)
Please post DDL, so that people do not have to guess what the keys, constraints, Declarative Referential Integrity, data types, etc. in your schema are. Learn how to follow ISO-11179 data element naming conventions and formatting rules. Temporal data should use ISO-8601 formats. Code should be in Standard SQL as much as possible and not local dialect.
This is minimal behavior on SQL forums. Putting “tbl_” on table name is a classic design flaw called “tbling” and the column names are violations of ISO-11179 rules, too. Now we have to guess at keys, data types, etc. Here is my guess and clean up.
CREATE TABLE Prizes
(prize_id INTEGER NOT NULL PRIMARY KEY,
prize_name CHAR(1) NOT NULL,
prize_rank INTEGER NOT NULL);
INSERT INTO Prizes
VALUES
(1, 'A', 1),
(2, 'B', 2),
(3, 'C', 3),
(4, 'D', 4),
(5, 'E', 5);
Why triggers? RDBMS has virtual tables and columns. This not a deck of punch cards or a magnetic tape file. A VIEW is always current and correct.
CREATE VIEW Prize_List
AS
SELECT prize_id, prize_name,
ROW_NUMBER() OVER (ORDER BY prize_id)
AS prize_rank
FROM Prizes;
But it might be better to drop the prize_id column completely and re-arrange the display order based on the prize_rank column:
CREATE TABLE Prizes
(prize_name CHAR(1) NOT NULL,
prize_rank INTEGER NOT NULL PRIMARY KEY);
Now use procedures to manipulate the table as needed.
CREATE PROCEDURE Swap_Prize_Ranks (#old_prize_rank INTEGER, #new_prize_rank INTEGER)
AS
UPDATE Prizes
SET prize_rank
= CASE prize_rank
WHEN #old_prize_rank
THEN #new_prize_rank
ELSE prize_rank + SIGN(#old_prize_rank - #new_prize_rank)
END
WHERE prize_rank BETWEEN #old_prize_rank AND #new_prize_rank
OR prize_rank BETWEEN #new_prize_rank AND #old_prize_rank;
When you want to drop a few rows, remember to close the gaps with this:
CREATE PROCEDURE Close_Prize_Gaps()
AS
UPDATE Prizes
SET prize_rank
= (SELECT COUNT (P1.prize_rank)
FROM Prizes AS P1
WHERE P1.prize_rank <= Prizes.prize_rank);