Collation: Expression

Leave a comment

March 26, 2014 by Kenneth Fisher

I had a recent run in with collation problems and it got me started reading. As I read I started to realize that for a seemingly simple subject there was a lot to it. So I thought I would go over some of what I found out.

Once you have installed your instance, created your database and tables you are now ready to start running queries. This is the point where you might have to change collations at an expression level. In order to make this change you use the COLLATE clause. This clause can be used after any string column or variable in a query. For example let’s say you have a table as such:

-- Create table with a column with a Case Insensative collation
CREATE TABLE Collate_Test (
	Id int NOT NULL IDENTITY(1,1),
	Name varchar(50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL 
	);
-- Insert a list of the same name but different cases
INSERT INTO Collate_Test VALUES
	('kenneth'),
	('Kenneth'),
	('KENneth'),
	('KENNEth'),
	('KENNETH'),
	('fisher'),
	('Fisher'),
	('FISher'),
	('FISHer'),
	('FISHER');
GO

When you run the query

SELECT *
FROM Collate_Test
ORDER BY Name;
GO

You should get the following result. Note the order of the identity column. I put it in there to help see the sort difference.

CollationExpression1

But now you want a case sensitive sort by name.

SELECT *
FROM Collate_Test
ORDER BY Name COLLATE SQL_Latin1_General_CP1_CS_AS;
GO

Note that the order of the column has changed. Again the identity column is there to help see the sort difference.

CollationExpression2

Now let’s add a variable @Name. When we run the following query without the COLLATE clause we get all of the “kenneth” rows back.

DECLARE @Name varchar(50);
SET @Name = 'Kenneth';

SELECT *
FROM Collate_Test
WHERE Name = @Name;
GO

CollationExpression3

But if we add the collate clause to make the variable case sensitive we get rather different results.

DECLARE @Name varchar(50);
SET @Name = 'Kenneth';

SELECT *
FROM Collate_Test
WHERE Name = @Name COLLATE SQL_Latin1_General_CP1_CS_AS;
GO

CollationExpression4

You should be aware that I could have put the COLLATE clause on the column instead of the variable or on both the column and the variable and it would have worked just fine.


Over a number of different posts I’m going to discuss some of the surprisingly deep subject of collation.

As a start listen to Rob Farley’s hilarious talk on collation
Collation: Definition
Collation: Location
Collation: Correction -> Expression, Column, Database
Collation: Correction -> Instance
Collation: Temporary objects & variables: Demonstration
Collation: Confusion

About these ads

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 300 other followers

%d bloggers like this: