SQL Server 2012 : Ordering the Result Set (part 1) - Specifying the ORDER BY Using Column Names, Specifying the ORDER BY Using Expressions

Logically, relational data should always be considered an unordered list. The primary key's purpose is to uniquely identify the row, not sort the table. SQL Server usually returns the data in the order of the primary key (because that's probably the clustered index), but there's no logical guarantee of that order. The only correct way to sort the results is with an ORDER BY clause.

SQL can sort by multiple columns, and the sort columns don't have to be columns that are returned by the SELECT, so there's a lot of flexibility in how you can specify the columns. Using Management Studio's Query Designer, you can create the ORDER BY by selecting the sort order for the column, as shown in Figure 1.

Figure 1 Within Management Studio's Query Designer, you can define the sort order and sort type in the column pane. The TOP() predicate is set for the Query Designer inside the query's Properties page.

Although there is not a limit on the number of columns that you can specify in the ORDER BY clause of the select statement, an internal operation exists that indirectly enforces a limit.

Specifying the ORDER BY Using Column Names

The best way to sort the result set is to completely spell out the ORDER BY columns:

USE AdventureWorks;

SELECT FirstName, LastName
 FROM Person.Person

ORDER BY LastName, FirstName;

Result:

FirstName   LastName
------------- --------------------
Syed     Abbas
Catherine   Abel
Kim      Abercrombie
. . .

Specifying the ORDER BY Using Expressions

In the case of sorting by an expression, you can repeat the entire expression in the ORDER BY clause. This does not cause a performance hit because the SQL Server Query Optimizer is smart enough to avoid recomputing the expression:

SELECT
LastName + ‘, ‘ + FirstName AS FullName
 FROM Person.Person
 ORDER BY LastName + ‘, ‘ + FirstName;

Result:

FullName
----------------------
Abbas, Syed
Abel, Catherine
Abercrombie, Kim
. . .

Using an expression in the ORDER BY clause can solve some headaches. For example, some database developers store product titles in two columns: One column includes the full title, and the duplicate column stores the title stripped of the leading “The.” In terms of performance, such denormalization might be a good idea, but using a case expression within the ORDER BY clause correctly sorts without duplicating the title.

The AdventureWorks sample database includes a list of Product Descriptions. If the Description includes a leading “This,” then the CASE expression removes it from the data and passes to the ORDER BY:

USE AdventureWorks;
SELECT Description, LEN(Description) AS TextLength
FROM Production.ProductDescription
WHERE
   Description LIKE ‘Replacement%'
ORDER BY
CASE
   WHEN LEFT(Description, 5) = ‘This ‘
   THEN Stuff(Description, 1, 5, ‘')
ELSE
   Description
END;

Result:

Description                        TextLength
---------------------------------             ----------
Replacement mountain wheel for entry-level rider.         49
Replacement mountain wheel for entry-level rider.         49
Replacement mountain wheel for the casual to serious rider.    59
Replacement mountain wheel for the casual to serious rider.    59
Replacement rear mountain wheel for entry-level rider.       54
Replacement rear mountain wheel for the casual to serious rider.  64
Replacement rear wheel for entry-level cyclist.          47
Replacement road front wheel for entry-level cyclist.       53
Replacement road rear wheel for entry-level cyclist.        52
. . .