Reverse of each value in a column - sql-server

Question

Suppose I have a table with even number of rows. For eg- a table Employee with two columns Name and EmpCode. The table looks like
Name EmpCode
Ajay 7
Vikash 5
Shalu 4
Hari 8
Anu 1
Puja 9
Now, I want my output in reverse of EmpCode like:
Name EmpCode
Ajay 9
Vikash 1
Shalu 8
Hari 4
Anu 5
Puja 7
I need to run this query in SQL Server.

Answer 1

As the OP hasn't replied, I'll post a little explanation for them instead. As everyone has eluded to, tables in SQL Server have no built in ordering. Your data is stored in what is known as a HEAP. This means, when you run a query without an ORDER BY your data can return in any order that the Server feels like. With small datasets this might be in the order you inserted it in, but that's just it (it might).
When you get to larger datasets, and when you have multiple cores running on the operation, then the order of a SELECT * FROM [Table]; is more likely to not be the order in insertion, and is more likely to be random which each instance of running the query. I have several tables where a SELECT TOP 1 *... will return a different row every time I run the query; even with the CLUSTERED INDEX.
The only, yes only, way to guarantee the order is by using ORDER BY. Now, you might have another column which you haven't shared that you can order by, but if not, perhaps this (very) simple example will at least assist you, if nothing else:
CREATE TABLE #Employee ([Name] varchar(10), EmpCode tinyint);
INSERT INTO #Employee
VALUES ('Ajay',7),
('Vikash',5),
('Shalu',4),
('Hari',8),
('Anu',1),
('Puja',9);
GO
--Just SELECT *. ORDER is NOT guaranteed, but, due to the low volume of data, will probably be in the order by insertion
SELECT *
FROM #Employee;
--But, we want to reverse the order, so, let's add an ORDER BY
SELECT *
FROM #Employee
ORDER BY [Name];
--Oh! That didn't work (duh). Let's try again
SELECT *
FROM #Employee
ORDER BY Empcode;
--Nope, this isn't working. That's because your data has nothing related to it's insertion order. So, let's give it one:
GO
DROP TABLE #Employee;
CREATE TABLE #Employee (ID int IDENTITY(1,1), --Oooo, what is this?
[Name] varchar(10),
EmpCode tinyint);
INSERT INTO #Employee
VALUES ('Ajay',7),
('Vikash',5),
('Shalu',4),
('Hari',8),
('Anu',1),
('Puja',9);
GO
--Now look
SELECT *
FROM #Employee;
--So, we can use an ORDER BY, and get the correct order too
SELECT [Name],
Empcode
FROM #Employee
ORDER BY ID;
--So, we got the right ORDER using an ORDER BY. Now we can do something about the ordering:
--We'll need a CTE for this:
WITH RNs AS(
SELECT *,
ROW_NUMBER() OVER (ORDER BY ID ASC) AS RN1,
ROW_NUMBER() OVER (ORDER BY ID DESC) AS RN2
FROM #Employee)
SELECT R1.[Name],
R2.EmpCode
FROM RNs R1
JOIN RNs R2 ON R1.RN1 = R2.RN2;
GO
DROP TABLE #Employee;