Change Position of Serial Number in SQL - sql

Question

I have a table named students. the structure is given below
______________________________
AdmissionNo RollNo Name
______________________________
1001 1 A
1003 2 B
1005 3 C
1006 4 D
1008 5 E
Now i want to change rollno 4 to 2 and increment forthcoming numbers
so the result should be like below
-------------------------------
AdmissionNo RollNo Name
-------------------------------
1001 1 A
1006 2 D
1003 3 B
1005 4 C
1008 5 E
--------------------------------
How to attain this using sql Query.
Note: Question Edited as per 'The Impaler' said.Admission number is not changing.only Roll no change. The values in table are examples actual values are hundreds of records.

Answer 1

With the omission of a dialect, I have answered this in T-SQL, as I wanted a stab at this.
This isn't pretty, however, I use a couple of updatable CTE's to find the offset for the specific rows, and then update the needed rows accordingly:
USE Sandbox;
GO
CREATE TABLE dbo.YourTable (AdmissionNo int, Rollno tinyint, [Name] char(1));
INSERT INTO dbo.YourTable
VALUES(1001,1,'A'),
(1003,2,'B'),
(1005,3,'C'),
(1006,4,'D'),
(1008,5,'E');
GO
DECLARE #NewPosition tinyint = 2,
#MovingName char(1) = 'D';
WITH Offsetting AS(
SELECT *,
COUNT(CASE Rollno WHEN #NewPosition THEN 1 END) OVER (ORDER BY RollNo ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING) -
COUNT(CASE [Name] WHEN #MovingName THEN 1 END) OVER (ORDER BY RollNo ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING) AS LagOffset
FROM dbo.YourTable),
NewNames AS(
SELECT *,
CASE RollNo WHEN #NewPosition THEN #MovingName
ELSE LAG([Name],LagOffset) OVER (ORDER BY RollNo)
END AS NewName
FROM Offsetting)
UPDATE NewNames
SET [Name] = NewName;
GO
SELECT *
FROM dbo.YourTable;
GO
DROP TABLE dbo.YourTable;

Answer 2

Not pretty but you could use some sub queries
DROP TABLE IF EXISTS T;
create table t
(AdmissionNo int, RollNo int, Name varchar(1));
insert into t values
(1001 , 1 , 'A'),
(1003 , 2 , 'B'),
(1005 , 3 , 'C'),
(1006 , 4 , 'D'),
(1008 , 5 , 'E');
select t.*,
case when rollno = 2 then (select name from t where rollno = 4)
when rollno > 2 and
rollno <> (select max(rollno) from t) then (select name from t t1 where t1.rollno < t.rollno order by t1.rollno desc limit 1)
else name
end
from t;
+-------------+--------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 1001 | 1 | A | A |
| 1003 | 2 | B | D |
| 1005 | 3 | C | B |
| 1006 | 4 | D | C |
| 1008 | 5 | E | E |
+-------------+--------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
5 rows in set (0.001 sec)

Answer 3

DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(admission_no INT NOT NULL PRIMARY KEY
,roll_no INT NOT NULL
,name CHAR(1) NOT NULL
);
INSERT INTO my_table VALUES
(1001,1,'A'),
(1003,2,'B'),
(1005,3,'C'),
(1006,4,'D'),
(1008,5,'E');
SELECT *
, CASE WHEN roll_no = 4 THEN 2
WHEN roll_no >= 2 AND roll_no < 4 THEN roll_no + 1
ELSE roll_no END x FROM my_table;
+--------------+---------+------+---+
| admission_no | roll_no | name | x |
+--------------+---------+------+---+
| 1001 | 1 | A | 1 |
| 1003 | 2 | B | 3 |
| 1005 | 3 | C | 4 |
| 1006 | 4 | D | 2 |
| 1008 | 5 | E | 5 |
+--------------+---------+------+---+
5 rows in set (0.00 sec)
...or, as an update...
UPDATE my_table x
JOIN
( SELECT *
, CASE WHEN roll_no = 4 THEN 2
WHEN roll_no >= 2 AND roll_no < 4 THEN roll_no + 1
ELSE roll_no END n
FROM my_table
) y
ON y.admission_no = x.admission_no
SET x.admission_no = y.n;
You'd probably want to extend this idea to deal with the fact that rows can be dragged up and down the list, so something like this...
SET #source = 1, #target = 5;
SELECT *
, CASE WHEN roll_no = GREATEST(#source,#target) THEN LEAST(#source,#target)
WHEN roll_no >= LEAST(#source,#target) AND roll_no < GREATEST(#source,#target) THEN roll_no + 1
ELSE roll_no END x
FROM my_table;

Answer 4

Try this below query
; with cte as (select a.AdmissionNo, a.RollNo, b.Name from student a
join student b on a.RollNo=b.RollNo+1
where a.RollNo between 3 and 4
union all
select a.AdmissionNo, a.RollNo, b.Name from student a
left join student b on a.RollNo+2=b.RollNo
where a.RollNo=2)
update a set a.Name = b.name
from student a
join cte b on a.rollno=b.rollno