t-sql

SQL Server Pagination

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Paging through data is something that developers need to do frequently.  Until SQL Server 2012, the best way to achieve this is with the ROW_NUMBER function… and let’s face it… that wasn’t the easiest/most elegant thing to use.  Our prayers have been answered in SQL Server 2012.  The SQL Server team has come out with a better way of doing pagination using the OFFSET FETCH clause.

 
The OFFSET FETCH Clause

The OFFSET FETCH clause allows the client application to pull only a specified range of records.  To implement pagination using the OFFSET FETCH clause, it takes two parts… the OFFSET and the FETCH. 🙂

NOTE: To use the OFFSET FETCH clause for pagination, you must use an ORDER BY clause as well.

 
OFFSET

This part tells SQL Server to skip N number of rows in the result set.

SELECT	*
FROM	Animal
ORDER	BY AnimalName ASC
OFFSET	50 ROWS

The above statement tells SQL Server to return all of the AnimalNames in the Animal table, but only return the names after the 50th.  So 51 and beyond.

 
FETCH

This part tells SQL Server how many records to return in the result set.  If you use FETCH, you always need to use OFFSET.

SELECT	*
FROM	Animal
ORDER	BY AnimalName ASC
OFFSET	50 ROWS
FETCH   NEXT 10 ROWS ONLY

The above statement tells SQL Server to return the AnimalNames in the Animal table with row numbers 51-60.  The OFFSET clause tells it to skip 50 rows and the FETCH clause tells it to return 10 records.

 
Variable Row Counts

You are also able to use a variable for the record counts in the query.  If you wanted to do this, it would look like this:

SELECT	*
FROM	Animal
ORDER	BY AnimalName ASC
OFFSET	@RowsToSkip ROWS
FETCH	NEXT @RowsToReturn ROWS ONLY

 
 
Reference: http://technet.microsoft.com/en-us/library/gg699618(v=sql.110).aspx

 

SQL Server Trim

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SQL Server trim function does not exist!  Although this seems a bit odd, SQL Server does somewhat have support for trimming data.  SQL Server has built in functions for Right Trim and for Left Trim.  Using these functions, you can accomplish a full trim.  I’ll first show you how to trim the different sides of the text and then show how to trim the full thing.

 
Trim Text Inline

The functions to trim text are RTrim() and LTrim().

DECLARE	@TextToTrim VARCHAR(50) = '     TEXT TO TRIM      '

-- Trims the spaces from the left side of the data
SELECT	LTRIM(@TextToTrim) AS LeftSpacesRemoved

-- Trims the spaces from the right side of the data
SELECT	RTRIM(@TextToTrim) AS RightSpacesRemoved

-- Trims the spaces from both sides of the data
SELECT	LTRIM(RTRIM(@TextToTrim)) AS FullTrim

 
If a full trim is something that you do often, you can create a SQL Server Trim function to make the process a little simpler.

CREATE	FUNCTION TRIM(@TextToTrim VARCHAR(8000))
RETURNS	VARCHAR(8000)
BEGIN

	RETURN	LTRIM(RTRIM(@TextToTrim))

END

You can use this new fancy SQL Server Trim function by calling it like this:

DECLARE	@TextToTrim VARCHAR(50) = '     TEXT TO TRIM      '

SELECT	dbo.TRIM(@TextToTrim) AS FullTrim

Cannot Insert Explicit Value For Identity Column

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If you try to insert in to a table with an ID column, you could get this error “Cannot insert explicit value for identity column in table ‘<<table>>’ when IDENTITY_INSERT is set to OFF.”  This is not the end of the world and is actually pretty easy to get around.

 
Why Are You Getting This Error?

The reason you’re getting this error is because you are trying to tell SQL Server what the ID value for a row in the table should be.  If you have an identity column on your table, SQL Server will want to generate that ID value for you automatically.  The error is essentially saying, “Hey, I’m supposed to generate the ID for you… you aren’t supposed to tell me what it is!”

 
How Can You Fix This?

There are two easy ways to get around this.

 
If You Want To Tell SQL Server What The ID Value Should Be

If want to specify what the ID values should be for the records you are inserting, then before you execute the INSERT statement, you need to run a small sql command to turn identity inserts on.  Identity inserts allow you to populate the value of an identity column with a specific value.

SET		IDENTITY_INSERT Animal ON

INSERT
INTO	Animal
		(AnimalID, AnimalName)
VALUES	(1,        'Horse'),
		(2,        'Pig'),
		(3,        'Cow')

SET		IDENTITY_INSERT Animal OFF

NOTE: You can only have identity insert on for one table at a time.  To insert in to a second table, you will need to turn the identity insert off on the first table before inserting in to the second table.

 
If You Want To Allow SQL Server To Generate The ID

If you don’t care about what the ID values are for these records, you should just allow SQL Server to generate the ID values for you.  To do this, just specify the columns that are in the table and leave off the identity column.

INSERT
INTO	Animal
		(AnimalName)
VALUES	('Horse'),
		('Pig'),
		('Cow')

 
Reference: http://msdn.microsoft.com/en-us/library/ms188059.aspx

Case Sensitive Compare

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Occasionally we need to do a string comparison in SQL Server as a case sensitive compare.  By default, case sensitive compare is not turned on for tables in SQL Server.  It’s actually pretty easy to change a string comparison to a case sensitive compare.  You can do this by using the COLLATE clause.

Read below to find out why this works and other tips on doing a case sensitive compare.

SELECT	A.AnimalID, A.AnimalName, AFT.FeedingTime
FROM	Animal A
INNER	JOIN AnimalFeedingTime AFT ON AFT.AnimalName = A.AnimalName COLLATE SQL_Latin1_General_CP1_CS_AS

 
 
What Is The COLLATE Clause

The COLLATE clause is something that you can add to the end of an expression to set the collation of the operation to a specific collation.  So in the example… the string equal comparison is being changed to a collation of SQL_Latin1_General_CP1_CS_AS.

A collation in SQL Server is something defines how data is compared.  This could be things like case sensitivity, acceptable characters, etc…  Most of the time (for English installations of SQL Server) it will be a collation type of SQL_Latin1_General_CP1_CI_AS.  This is because the Latin character set covers English and other Latin based languages.

The two most common collations that I deal with are SQL_Latin1_General_CP1_CI_AS and SQL_Latin1_General_CP1_CS_AS.  You can see that they are very similar.  In fact… the only difference is the _CI_ and _CS_.  These actually stand for Case-Insensitive and Case-Sensitive.
 
 
Field Level Case Sensitivity

Even better… you don’t need to set the collation on every sql statement that you want to make case sensitive.  There is actually a setting that you can apply to a field in a table.

NOTE: that if you are joining on this table, both collations must be the same or you will need to specify the collation to use.

Create a new table with a case sensitive field

CREATE
TABLE	Animal
(AnimalID		INT,
AnimalName	VARCHAR(100) COLLATE SQL_Latin1_General_CP1_CS_AS)

Change a table’s column to be case sensitive

ALTER
TABLE	Animals
ALTER	COLUMN AnimalName VARCHAR(100) COLLATE SQL_Latin1_General_CP1_CS_AS

Results In Random Order

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Although SQL Server does not have a built in way to return your query results in random order, you can accomplish this in an easy way.  One thing to note is that this way of returning the results is very expensive… so it could take a while.

In the following example, the magic happens in the order by clause.  The NEWID() function will generate a unique GUID for every record.  This will cause the results to come back randomized.

Syntax

SELECT FirstName,
       LastName
FROM   NameTable
ORDER  BY NEWID()