Friday, September 29, 2006

SQL Server Blog Of The Week: The SQL Doctor Is In (Real In) Louis Davidson

As I explained last week I will every Friday (not a promise) feature a SQL server related blog First up is The SQL doctor himself: Louis Davidson. I don't remember exactly how I found out about the existance of Louis Davidson, I am not sure anymore if it was from the WROX book or from the newsgroups. Not that it really matters since that red book has been replaced by a black and yellow one. Louis Davidson is the main author of Pro SQL Server 2005 Database Design and Optimization , a book I highly recommend

What do I like about this blog
I like the down to earth style which Louis uses. I also like the fact that Louis has some nice code on his blog that I can 'borrow' for my own needs. Another good thing is the fact that Louis tells you about any problems in the book and gives you either a workaround or expanded text that includes the things that are currently missing from the book. another thing that I like is the fact that Louis doesn't post about SQL Server only; you will also see posts about gadgets (Nintendo anyone?) and personal stuff

What are some at the posts I like the most
Query for Current Server Activity (2005)
Query locks being held (2005)
Monitor rollback progress (2005)
Query filegroups and indexes (2000,2005)

Where can I see/read/hear more about the author?
SQLDownUnder has a podcast with Louis Davidson and you can get it here, scroll down to episode 12
Louis also has some stuff on drsql.org; there you can find books that Louis finds useful, an index of his blog and more stuff

So there you have it; the SQL Server blog of the week

Trouble With ISDATE And Converting To SMALLDATETIME

If you want to use the ISDATE function to convert a value to a SMALLDATETIME you also have to take into consideration that SMALLDATETIME stores date and time data from January 1, 1900, through June 6, 2079 but DATETIME stores date and time data from January 1, 1753 through December 31, 9999
So even though the ISDATE function returns 1 for the date 1890-01-01 this can not be converted to SMALLDATETIME and you will receive an error message after you run the following statement

SELECT CONVERT(SMALLDATETIME,'18900101')

Server: Msg 296, Level 16, State 3, Line 1
The conversion of char data type to smalldatetime data type resulted in an out-of-range smalldatetime value.


Also be careful with rounding
Run these four statements
SELECT CONVERT(SMALLDATETIME,'2079-06-06 23:59:29')
SELECT CONVERT(SMALLDATETIME,'2079-06-06 23:59:29.998')
SELECT CONVERT(SMALLDATETIME,'2079-06-06 23:59:29.999')
SELECT CONVERT(SMALLDATETIME,'2079-06-06 23:59:30')


The first two are fine , the second two blow up because the value gets rounded up to the next day after it gets rounded up to the next minute (and hour)

I decided to roll out my own fnIsSmallDateTime() function because who wants to write the same CASE ISDATE when Value between this and that code all over the place?

Here is the code for the user defined function


CREATE FUNCTION fnIsSmallDateTime(@d VARCHAR(50))
RETURNS BIT
AS
BEGIN
DECLARE
@bitReturnValue BIT


SELECT @bitReturnValue =CASE
WHEN ISDATE(@d) = 1 THEN CASE
WHEN CONVERT(DATETIME,@d) > ='19000101'
AND CONVERT(DATETIME,@d) <= '20790606 23:59:29.998' THEN 1
ELSE 0
END
ELSE 0
END
RETURN
@bitReturnValue
END
GO


Let's create a test table with values
CREATE TABLE TestSmallDate (SomeDate VARCHAR(40))
INSERT TestSmallDate VALUES ('19000101')
INSERT TestSmallDate VALUES ('18991231')
INSERT TestSmallDate VALUES ('19010101')
INSERT TestSmallDate VALUES('20790607')
INSERT TestSmallDate VALUES ('2079-06-06 23:59:29.677')
INSERT TestSmallDate VALUES ('2079-06-06 23:59:29.998')
INSERT TestSmallDate VALUES ('2079-06-06 23:59:29.999')
INSERT TestSmallDate VALUES ('2079-06-06 23:59:59.000')
INSERT TestSmallDate VALUES('2079-06-06 01:00:00')
INSERT TestSmallDate VALUES ('2079-06-06 00:00:00')
INSERT TestSmallDate VALUES ('2079-06-06 00:00:01')
INSERT TestSmallDate VALUES('WhoIsYourDaddy')

If you want NULL for values that can not be converted to SMALLDATETIME use this code

SELECT dbo.fnIsSmallDateTime(SomeDate),
CASE dbo.fnIsSmallDateTime(SomeDate)
WHEN 1 THEN CONVERT(SMALLDATETIME,SomeDate) END AS ConvertedToSmallDate,
SomeDate
FROM TestSmallDate

if you want to convert the values that can not be converted to SMALLDATETIME to '1901-01-01 00:00:00' use the code below

SELECT dbo.fnIsSmallDateTime(SomeDate),
CASE dbo.fnIsSmallDateTime(SomeDate)
WHEN 1 THEN CONVERT(SMALLDATETIME,SomeDate)
ELSE CONVERT(SMALLDATETIME,'19000101') END AS ConvertedToSmallDate,
SomeDate
FROM TestSmallDate


Return only data that can be converted to SMALLDATETIME

SELECT * FROM TestSmallDate
WHERE dbo.fnIsSmallDateTime(SomeDate) =1



Return only data that can not converted to SMALLDATETIME

SELECT * FROM TestSmallDate
WHERE dbo.fnIsSmallDateTime(SomeDate) =0

SQL Server Application Platform Podcast About SQL Server Service Broker On Channel 9

Channel 9 has a two part podcast with Roger Wolter about SQL Server Service Broker. WMA, MP3 and Video formats are available for download

From the site: "You are thinking of a messaging solution for your application. A solution that can exchange messages reliably, predictably and in-order. A solution that offers queue like functionality only better. What is it you ask? None other than SQL Server 2005 and this very interesting technology known as SQL Service Broker that is built right into it. On today’s program I’m joined by my colleague Roger Wolter who is going to give us all the juicy details"

Get the episodes here --> part1, part2

Wednesday, September 27, 2006

Cool And Sexy New SQL Server Blog

That's right! What is more cool or sexy than Query Optimizations? It doesn't matter how beautiful or complex your data model is, if you show to your boss that a query used to take 17 seconds and now runs in 300 milli-seconds then you are the new SQL superhero.

If some of the following terms are foreign to you (CTRL + K, Index Scan, Index Seek, Table Scan, Sargable, Index Hint, Parameter Sniffing, Missing Statistics, L2 Cache, Compilation, Optimal Plans) then I have the blog for you right here
Tips, Tricks, and Advice from the SQL Server Query Processing Team
Even if you do know about those terms then this is still the blog for you since there is tons of stuff that you did not know yet. so make sure to check it out and add it to your feed

Tuesday, September 26, 2006

Return A Rowcount By Using Count Or Sign

Sometimes you are asked by the front-end/middle-tier developers to return a rowcount as well with the result set. However the developers want you to return 1 if there are rows and 0 if there are none. How do you do such a thing?
Well I am going to show you two ways. the first way is by using CASE and @@ROWCOUNT, the second way is by using the SIGN function

For CASE we will do this

RETURN CASE WHEN @@ROWCOUNT > 0 THEN 1 ELSE 0 END

So that's pretty simple, if @@ROWCOUNT is greater than 0 return 1 for everything else return 0

Using the SIGN function is even easier, all you have to do is this

RETURN SIGN(@@ROWCOUNT)

That's all, SIGN Returns the positive (+1), zero (0), or negative (-1) sign of the given expression. In this case -1 is not possible but the other two values are
So let's see this in action


USE pubs
GO

--Case Proc
CREATE PROCEDURE TestReturnValues
@au_id VARCHAR(49) ='172-32-1176'
AS
SELECT
*
FROM authors
WHERE au_id =@au_id

RETURN CASE WHEN @@ROWCOUNT > 0 THEN 1 ELSE 0 END
GO

--Sign Proc
CREATE PROCEDURE TestReturnValues2
@au_id VARCHAR(49) ='172-32-1176'
AS
SELECT
*
FROM authors
WHERE au_id =@au_id

RETURN SIGN(@@ROWCOUNT)
GO


--Case Proc, 1 will be returned; default value is used
DECLARE @Rowcount int
EXEC @Rowcount = TestReturnValues
SELECT @Rowcount
GO

--Case Proc, 0 will be returned; dummy value is used
DECLARE @Rowcount int
EXEC @Rowcount = TestReturnValues 'ABC'
SELECT @Rowcount
GO

--Sign Proc, 1 will be returned; default value is used
DECLARE @Rowcount int
EXEC @Rowcount = TestReturnValues2
SELECT @Rowcount
GO

--Sign Proc, 0 will be returned; dummy value is used
DECLARE @Rowcount int
EXEC @Rowcount = TestReturnValues2 'ABC'
SELECT @Rowcount
GO


--Help the environment by recycling ;-)
DROP PROCEDURE TestReturnValues2,TestReturnValues
GO

Monday, September 25, 2006

Happy One Year Anniversary

So here we are one year and 236 posts later. I can not believe that it has been one year already. First of all I will make 2 small changes. The first change is that I will feature a blog/site of the week; this will always happen on a Friday. I will link to the blog and link to the 5 most interesting posts/articles. If possible I will say a little something about the person whose site it is, something like author of this book and an interview is available here.

The second change is that I will write some stuff that has nothing to do with SQL Server but might still be of interest to you. This I will publish on weekends so that you can skip that easily if you check on weekdays only. What will I write? Maybe something that goes on in my life or a book or movie review. However I will not review the Matrix, Titanic or some other well know movie. No I will pick something that is not as popular for example Ghost In The Machine, The Seven Samurai, Animatrix. For books this could be Crypto, The Cobra Event or The Coming Plague

Or I could write that once you have kids and you do NOT have TIVO then Comcast On Demand really rocks. For example Jericho is a show that I just started to watch, this show reminded me a little bit of The Stand by Stephen King (his best book together with Thinner, It and Salems Lot)
So what is so cool about On Demand? No commercials, that’s right; nada. Pause and Resume for up to 24 hours, this is a must have with newborns.

Comcast announced a deal with CBS to have the following shows free the day after it airs: CSI: Crime Scene Investigation, CSI: Miami, CSI: NY, Survivor, NCIS, Numb3rs, Jericho and Big Brother

That’s it for now

Return All 78498 Prime Numbers Between 1 and 1000000 In 3 seconds

That is right folks; SQL Server is capable of returning all 78498 prime numbers between 1 and 1000000 in 3 seconds. Who said that SQL Server isn't suitable for this task?

Let's start with a little bit of history; Ward Pond had a posting on his blog on how to create a table with 1000000 rows. Hugo Kornelis replied with a solution that ran in 1110 ms. For fun I left the following comment: “How about the next challenge is to return all 78498 prime numbers between 1 and 1000000?”

Ward took the challenge and posted a solution that would take hours to complete. Then Hugo Kornelis posted a solution that took 8 seconds. After that Ward tweaked Hugo’s solution and got it down to 3 seconds. That is just unbelievable. I wonder how long it would run if you were to code something like that in C, C++, C# or your favorite language?

Any takers?

Wednesday, September 20, 2006

Five Ways To Return Values From Stored Procedures

I have answered a bunch of questions over the last couple of days and some of them had to do with returning values from stored procedures
Everyone knows that you can return a value by using return inside a stored procedure. What everyone doesn't know is that return can only be an int data type
So how do you return something that is not an int (bigint, smallint etc etc) datatype
Let's take a look
We will start with a regular return statement, everything works as expected

--#1 return
CREATE PROCEDURE TestReturn
AS
SET NOCOUNT ON

DECLARE
@i int
SELECT @i = DATEPART(hh,GETDATE())
RETURN @i
SET NOCOUNT OFF
GO

DECLARE @SomeValue int
EXEC @SomeValue = TestReturn
SELECT @SomeValue
GO


Now let's try returning a varchar

ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON

DECLARE
@i VARCHAR(50)
SELECT @i = DATENAME(mm,GETDATE())
RETURN @i
SET NOCOUNT OFF
GO

DECLARE @SomeValue VARCHAR(50)
EXEC @SomeValue = TestReturn
SELECT @SomeValue
GO

Oops, it doesn't work the following message is returned (if you run it in September)
Server: Msg 245, Level 16, State 1, Procedure TestReturn, Line 7
Syntax error converting the varchar value 'September' to a column of data type int.

Let's try hard coding a character value
ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON
RETURN
'ab'
SET NOCOUNT OFF
GO


DECLARE @SomeValue VARCHAR(50)
EXEC @SomeValue = TestReturn
SELECT @SomeValue
GO

It is interesting that the procedure compiles without a problem. But when we try to run it the following message is displayed


Server: Msg 245, Level 16, State 1, Procedure TestReturn, Line 7
Syntax error converting the varchar value 'ab' to a column of data type int.


So what can we do? well we can use an OUTPUT parameter. By the way the following 4 ways to return a varchar values are in the order from best to worst

--#2 OUTPUT
ALTER PROCEDURE TestReturn @SomeParm VARCHAR(50) OUTPUT
AS
SET NOCOUNT ON
SELECT
@SomeParm = 'ab'
SET NOCOUNT OFF
GO


DECLARE @SomeValue VARCHAR(50)
EXEC TestReturn @SomeParm = @SomeValue OUTPUT
SELECT @SomeValue
GO


Another way is to create a temp table and call the proc with insert..exec

--#3 Insert Into TEMP Table outside the proc
ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON
SELECT
'ab'
SET NOCOUNT OFF
GO

DECLARE @SomeValue VARCHAR(50)
CREATE TABLE #Test(SomeValue VARCHAR(50))
INSERT INTO #Test
EXEC TestReturn
SELECT @SomeValue = SomeValue
FROM #Test

SELECT @SomeValue
DROP TABLE #Test
GO


This one is almost the same as the previous example, the only difference is that ther insert happens inside the proc
And of course if you call the proc without creating the table you will get a nice error message

--#4 Insert Into TEMP Table inside the proc
ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON
INSERT INTO
#Test
SELECT 'ab'
SET NOCOUNT OFF
GO


DECLARE @SomeValue VARCHAR(50)
CREATE TABLE #Test(SomeValue VARCHAR(50))
EXEC TestReturn
SELECT @SomeValue = SomeValue
FROM #Test

SELECT @SomeValue
DROP TABLE #Test


And last you create a permanent table with an identity, in the proc you insert into that table and you return the identity value. You can then use that identity value to get the varchar value

--#5 Insert Into A Table And Return The Identity value
CREATE TABLE HoldingTable(ID INT IDENTITY,SomeValue VARCHAR(50))
GO

ALTER PROCEDURE TestReturn
AS
SET NOCOUNT ON
DECLARE
@i INT

INSERT INTO HoldingTable
SELECT 'ab'
SELECT @I = SCOPE_IDENTITY()

RETURN @i
SET NOCOUNT OFF
GO

DECLARE @SomeValue VARCHAR(50), @i INT
EXEC @i = TestReturn
SELECT @SomeValue = SomeValue
FROM HoldingTable
WHERE ID = @i

SELECT @SomeValue



DROP PROCEDURE TestReturn

Tuesday, September 19, 2006

You Can Rollback Tables That You Have Truncated (Inside A Transaction)

There seems to be a misconception that when you issue a TRUNCATE command against a table you will not be able to roll back.
That simply is not true; TRUNCATE TABLE removes the data by deallocating the data pages used to store the table's data, and only the page deallocations are recorded in the transaction log.
What does this mean? This means that SQL Server will use the mimimum amount of logging that it can to delete the data and still make it recoverable. in contrast to that the DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row

You see why TRUNCATE is so much faster; it deals with pages not with rows. and we all know that 1 extent is 8 pages and a page is 8K and can hold 8060 bytes. Well if you rows are 20 bytes wide then you need to log 403 delete statements with DELETE but TRUNCATE just uses a pointer to the page

So let's see how that works

--Create the table and inser 6 values
CREATE TABLE RollBacktest(id INT)
INSERT RollBacktest VALUES( 1 )
INSERT RollBacktest VALUES( 2 )
INSERT RollBacktest VALUES( 3 )
INSERT RollBacktest VALUES( 4 )
INSERT RollBacktest VALUES( 5 )
INSERT RollBacktest VALUES( 6 )
GO

--Should be 6 rows
SELECT 'Before The Transaction',* FROM RollBacktest

BEGIN TRAN RollBackTestTran
TRUNCATE TABLE RollBacktest

--Should be empty resultset
SELECT * FROM RollBacktest

--should be 0
SELECT COUNT(*) AS 'TruncatedCount' FROM RollBacktest

ROLLBACK TRAN RollBackTestTran

--Yes it is 6 again
SELECT 'ROLLED BACK',* FROM RollBacktest

DROP TABLE RollBacktest

SQL Server Podcast With Solid Quality Learning Mentor Peter Myers

SQL Down Under has announced their latest podcast with guest Peter Myers.
SQL Server podcast show 19 with Solid Quality Learning mentor Peter Myers. In this show, Peter provides an introduction to SQL Server Analysis Services for developers and DBA's.


Get the podcast from SQL Down Under

Monday, September 18, 2006

DDL Trigger Events Documented In Books On Line

A while back I wrote about DDL trigger events in a post named DDL Trigger Events Revisited
And I claimed that this stuff wasn't documented
Well I am wrong, this information is documented in the Books Online topic "Event Groups for Use with DDL Triggers.

The link to the online Books On Line is below
http://msdn2.microsoft.com/en-us/library/ms191441.aspx


Anyway they have an image, at least you can copy and paste the code I gave you ;-)

Friday, September 15, 2006

Do Not Concatenate VARCHAR and VARCHAR(MAX) Variables

Do Not Concatenate VARCHAR and VARCHAR(MAX) Variables, what happens is that the whole string will be implicitly converted to varchar(8000)

Run these examples to see what I mean

declare @v varchar(max)
select @v = (cast('a' as varchar)) + replicate('a', 9000)

select len(@v)
--8000
GO

declare @v varchar(max)
select @v = (cast('a' as varchar(1))) + replicate('a', 9000)

select len(@v)
--8000
GO

declare @v varchar(max)
select @v = (cast('a' as varchar)) +replicate (cast('a' as varchar(max)), 9000)

select len(@v)
--9001
GO

declare @v varchar(max)
select @v = (cast('a' as varchar(1))) + replicate(cast('a' as varchar(max)), 9000)

select len(@v)
--9001
GO


Or how about this? If you don't convert to varchar(max) while doing the LEN function it returns 8000

declare @v varchar(max)
select @v = replicate('a', 9000)
select len(@v)


declare @v varchar(max)
select @v = replicate(cast('a' as varchar(max)), 9000)
select len(@v)

Thursday, September 14, 2006

O'Reilly Code Search

Here is something handy:

Announcing O'Reilly Code Search, where you can enter search terms to find relevant sample code from nearly 700 O'Reilly books. The database currently contains over 123,000 individual examples, comprises 2.6 million lines of code, all edited and ready to use.


it's pretty neat, all the source code from all the O'Reilly books is searchable online

So to Search for the term SELECT in category SQL you would enter "cat:sql select" and this would return these results http://labs.oreilly.com/search.xqy?t=code&q=cat%3Asql+select

For C# you would do "cat:csharp select" and just SQL Server instead of SQL would be "cat:sql server select"

Let me know what you think

Wednesday, September 13, 2006

What Is Your Corporate Standard

If you are not a consultant and you work for a company then does your company have a corporate standard for development languages/products?
Our IT department is about 800 people and to get good support you can not have 3 thousands different products in your shop. As of today this is what is supported in our company

Java Stack
Sun's Project Tango
Apache Web Server 2.x
Tomcat 5.x (web container), JBoss 4.x (EJB and Web Container), WebSphere Network Edition 6.1.x (web and EJB container)
Hibernate 2.x, Spring 1.2.x
Sun's J2SE 5 (aka J2SE 1.5.x)
MySQl 5.x, Oracle 10g, SQL Server 2005

.NET Stack
WCF
IIS 6
.NET 2.0
CLR Version 2
MySQl 5.x, Oracle 10g, SQL Server 2005

Of course we have other things that we use ColdFusion, SQL Server 2000, that is fine but no NEW development is supposed to be done with those tools/products

So here is my question to you; what is your corporate standard?

The sum or average aggregate operation cannot take a bit data type as an argument

The sum or average aggregate operation cannot take a bit data type as an argument.
Oh yes I fell for this one yesterday. It's not that I didn't know about it (in the back of my head) it's just that I forgot
I was answering one question in the microsoft forums and someone wanted to sum something, unfortunately the datatype was bit and as we all know bit data types can not be used with average or sum.

You see that's why it is important when asking question to provide DDL and INSERT scripts. If I had that then I would have gotten the error myself and would have modified the query by converting to int

So instead of this (simplified)
SELECT SUM(col1)
FROM (SELECT CONVERT(BIT,1) AS col1 UNION ALL
SELECT CONVERT(BIT,0) )P

I would have done this
SELECT SUM(CONVERT(INT,col1))
FROM (SELECT CONVERT(BIT,1) AS col1 UNION ALL
SELECT CONVERT(BIT,0) )P


And of course we should all read this-->
http://classicasp.aspfaq.com/general/how-do-i-make-sure-my-asp-question-gets-answered.htm l

Does this qualify as a rant? I hope not.

Sunday, September 10, 2006

sys.dm_db_index_usage_stats

This is the second article about the dynamic managment views in SQL Server 2005, to see all of them click here

Today we are going to talk about the sys.dm_db_index_usage_stats dynamic managment view
This view is extremely helpful in a couple of ways, I will list some of them
It can help you identify if an index is used or not
You can also find out the scan to seek ratio
Another helpful thing is the fact that the last seek and scan dates are in the view, this can help you determine if the index is still used


So let's get started shall we?


CREATE TABLE TestIndex(id INT identity,
SomeID INT not null,
SomeDate DATETIME not null)
GO

CREATE CLUSTERED INDEX IX_TestIndexID ON TestIndex(SomeID)
GO

CREATE NONCLUSTERED INDEX IX_TestIndexDate ON TestIndex(SomeDate)
GO

INSERT TestIndex VALUES(1,GETDATE())
GO
INSERT TestIndex VALUES(2,GETDATE()-1)
GO


--Run the sys.dm_db_index_usage_stats query
SELECT
TableName = OBJECT_NAME(s.[object_id]),
IndexName = i.name,
s.last_user_seek,
s.user_seeks,
CASE s.user_seeks WHEN 0 THEN 0
ELSE s.user_seeks*1.0 /(s.user_scans + s.user_seeks) * 100.0 END AS SeekPercentage,
s.last_user_scan,
s.user_scans,
CASE s.user_scans WHEN 0 THEN 0
ELSE s.user_scans*1.0 /(s.user_scans + s.user_seeks) * 100.0 END AS ScanPercentage,
s.last_user_lookup,
s.user_lookups,
s.last_user_update,
s.user_updates,
s.last_system_seek,
s.last_system_scan,
s.last_system_lookup,
s.last_system_update,*
FROM
sys.dm_db_index_usage_stats s
INNER JOIN
sys.indexes i
ON
s.[object_id] = i.[object_id]
AND s.index_id = i.index_id
WHERE
s.database_id = DB_ID()
AND OBJECTPROPERTY(s.[object_id], 'IsMsShipped') = 0
AND OBJECT_NAME(s.[object_id]) = 'TestIndex';

After each of the select queries below run the sys.dm_db_index_usage_stats query above

--user_updates should be 2 but user_seeks,user_scans, user_lookups should be 0
SELECT *
FROM TestIndex
WHERE ID =1
--IX_TestIndexID user_scans = 1


SELECT *
FROM TestIndex
WHERE SomeID =1
--IX_TestIndexID user_seeks = 1

SELECT *
FROM TestIndex
WHERE SomeDate > GETDATE() -1
AND SomeID =1
--IX_TestIndexID user_seeks = 2


--let's force the optimizer to use the IX_TestIndexDate index

SELECT *
FROM TestIndex WITH (INDEX = IX_TestIndexDate)
WHERE SomeDAte > GETDATE() -1
--IX_TestIndexDate user_seeks = 1


IX_TestIndexID
SeekPercentage = 66.66% and ScanPercentage = 33.33

As you can see I have added the following code
CASE s.user_seeks WHEN 0 THEN 0
ELSE s.user_seeks*1.0 /(s.user_scans + s.user_seeks) * 100.0 END AS SeekPercentage
CASE s.user_scans WHEN 0 THEN 0
ELSE s.user_scans*1.0 /(s.user_scans + s.user_seeks) * 100.0 END AS ScanPercentage

This is helpful to determine the seek/scan ratio if you have mostly scans then maybe you have to look at your queries to optimize them


If you run the sys.dm_db_index_usage_stats query again you will se that the user_updates column is 2, that's because we inserted 2 rows (2 batches)

Let's do this

UPDATE TestIndex
SET SomeID = SomeID + 1
--(2 row(s) affected)

Now user_updates is 3 since we used 1 batch that modified 2 rows

Now restart your server and run the same query again. as you can see the resultset is empty this is because the counters are initialized to empty whenever the SQL Server (MSSQLSERVER) service is started. In addition, whenever a database is detached or is shut down (for example, because AUTO_CLOSE is set to ON), all rows associated with the database are removed.
When an index is used, a row is added to sys.dm_db_index_usage_stats if a row does not already exist for the index. When the row is added, its counters are initially set to zero.

When you run this query

SELECT *
FROM TestIndex

You will see a row again after you run the sys.dm_db_index_usage_stats query
Also note that every individual seek, scan, lookup, or update on the specified index by one query execution is counted as a use of that index and increments the corresponding counter in this view. Information is reported both for operations caused by user-submitted queries, and for operations caused by internally generated queries, such as scans for gathering statistics.

The user_updates counter indicates the level of maintenance on the index caused by insert, update, or delete operations on the underlying table or view. You can use this view to determine which indexes are used only lightly all by your applications. You can also use the view to determine which indexes are incurring maintenance overhead. You may want to consider dropping indexes that incur maintenance overhead, but are not used for queries, or are only infrequently used for queries.


sys.dm_db_index_usage_stats

database_id smallint
ID of the database on which the table or view is defined.

object_id int
ID of the table or view on which the index is defined

index_id int
ID of the index.

user_seeks bigint
Number of seeks by user queries.

user_scans bigint
Number of scans by user queries.

user_lookups bigint
Number of lookups by user queries.

user_updates bigint
Number of updates by user queries.

last_user_seek datetime
Time of last user seek

last_user_scan datetime
Time of last user scan.

last_user_lookup datetime
Time of last user lookup.

last_user_update datetime
Time of last user update.

system_seeks bigint
Number of seeks by system queries.

system_scans bigint
Number of scans by system queries.

system_lookups bigint
Number of lookups by system queries.

system_updates bigint
Number of updates by system queries.

last_system_seek datetime
Time of last system seek.

last_system_scan datetime
Time of last system scan.

last_system_lookup datetime
Time of last system lookup.

last_system_update datetime
Time of last system update.

Saturday, September 09, 2006

Don't Use Union On Tables With Text Columns

When you have a SQL UNION between 2 or more tables and some of these tables have columns with a text data type use UNION ALL instead of UNION.
If you use UNION you will be given the following message

Server: Msg 8163, Level 16, State 4, Line 10
The text, ntext, or image data type cannot be selected as DISTINCT.

What happens is that UNION use distinct behind the scenes and you can not use distinct on text, ntext or image data types

Run this script to see what I mean

CREATE TABLE TestUnion1 (id INT,textCol TEXT)
CREATE TABLE TestUnion2 (id INT,textCol TEXT)
GO

INSERT TestUnion1 VALUES(1,'abc')
INSERT TestUnion2 VALUES(1,'abc')
INSERT TestUnion1 VALUES(1,'aaa')
INSERT TestUnion1 VALUES(1,'zzz')
INSERT TestUnion1 VALUES(3,'abc')


--problem
SELECT * FROM TestUnion1
UNION --ALL
SELECT * FROM TestUnion2


--no problem
SELECT * FROM TestUnion1
UNION ALL
SELECT * FROM TestUnion2


DROP TABLE TestUnion1,TestUnion2

Thursday, September 07, 2006

SQL Server 2005 Failover Clustering White Paper

Microsoft has published a comprehensive document about implementing failover clustering for SQL Server 2005 and Analysis Services

Overview
This white paper is intended for a technical audience and not technical decision makers. It complements the existing documentation around planning, implementing, and administering of a failover cluster that can be found in Microsoft SQL Server 2005 Books Online. To ease the upgrade process for existing users of failover clustering, this white paper also points out differences in the failover clustering implementation of SQL Server 2005 compared to SQL Server 2000.


Get it here

Kalen Delaney Has Finished Inside SQL Server 2005: The Storage Engine And Is Also Blogging On SQLblog.com

Some good news that I am very excited about; Kalen Delaney has finished Inside SQL Server 2005: The Storage Engine. I have already pre-ordered her book but will have to wait until November 8, 2006 when it will ship (hopefully). I have her 2000 edition and it's my favorite book together with Ken Henderson's Guru series. Kalen also has started to blog on SQLblog.com

So what am I currently reading and what else am I going to buy.
Currently I am reading a very good SQL book by Louis Davidson named Pro SQL Server 2005 Database Design and Optimization. I hope to be done by the time Inside SQL Server 2005: The Storage Engine ships, I should be if the kids let me. Pro SQL Server 2005 Database Design and Optimization is a very good book and starts from Data Model and goes all the way to Database Interoperability. some other things covered are Protecting the Integrity of Your Data,Table Structures and Indexing,Coding for Concurrency
This book does also a very good job of explaining Codd’s 12 Rules for an RDBMS

What am I going to buy next?
Next book on my list is Expert SQL Server 2005 Development by Adam Machanic. I like the chapters that Adam wrote in Pro SQL server 2005, I like what he does in newsgroups and I like his blog. So that is enough for me to check out the book

After that I will buy SQL Server 2005 Practical Troubleshooting: The Database Engine by Ken Henderson which will be published December 5, 2006 (Sinterklaas dag for all you Dutch people)
I have 3 of Ken's books and I will get this one and the follow up to The Guru's Guide to SQL Server Stored Procedures, XML, and HTML which will be published May 31, 2007

So I went a little overboard with the links, this post has more blue characters than black ones.

So what is on your list and what are you currently reading?

I am also interested in getting A Developer's Guide to SQL Server 2005 by Bob Beauchemin. We will see; if I finish these books and the others are not published yet then I will. I did not have this problem when I used to take the Amtrak/NJ Transit train from Princeton to New York City (lots of time to read). Right now I work and live in Princeton and my commute is about 8 minutes

Wednesday, September 06, 2006

Microsoft SQL Server 2005 Everywhere Edition Access Database Synchronizer

Microsoft SQL Server 2005 Everywhere Edition Access Database Synchronizer provides a way to synchronize data between Microsoft Access database on a desktop and Microsoft SQL Server 2005 Everywhere Edition database on a device.

The setup installs the desktop component required for synchronizing Microsoft Access database with SQL Server Everywhere Edition database on the device. It also includes a read me file which has the documentation for the solution and a sample application. The sample application shows how the solution works and how to write applications for this solution. The components installed on the desktop can be used by third party applications to provide data synchronization between Microsoft Access database on the desktop and SQL Server Everywhere/SQL Mobile database on the device.

Download it here

Tuesday, September 05, 2006

Count Those Parentheses

This was a question on the microsoft.public.sqlserver.programming newsgroup, I thought it would be interesting to you to see wat i answered to this one
I believe that I have never used this many parenthese in my life before in a simple 2 column split

This is the question:
I have a column in a table that has multiple pieces of information in it that
I need to break out into various columns. The column is random but the
values I need to separate out are the number and the UN number as below:

245 HELIUM, COMPRESSED 2.2 UN1046


I need to separate the 2.2 and the UN1046 into different columns. How do I
parse this?



Here is the link to the original question at the microsoft.public.sqlserver.programming newsgroup


And here is my solution


CREATE TABLE Inventory (ItemDescription VARCHAR(99))
INSERT Inventory VALUES ('245 HELIUM, COMPRESSED 2.2 UN1046' )
INSERT Inventory VALUES ('24adada5 HELIsadasdadUM, sdsdsd 6.6 UN99' )
INSERT Inventory VALUES ('24adada5 HELIsadasdadUM, sdsdsd 446.6777 UN9988888' )
INSERT Inventory VALUES ('24adada5 HEdUM, sdsdsd 446.0 UN9988' )


SELECT RIGHT(ItemDescription,PATINDEX('% %',
REVERSE(ItemDescription))-1) AS COL1,
LTRIM(REVERSE(LEFT(REVERSE(LEFT(ItemDescription,(LEN(ItemDescription)-PATINDEX('% %', REVERSE(ItemDescription))))),
PATINDEX('% %',REVERSE(LEFT(ItemDescription,(LEN(ItemDescription)-PATINDEX('% %', REVERSE(ItemDescription)))))))))
AS COL2
FROM Inventory

SQL Server 2005 And SOA (Service-Oriented Architecture)

A white paper written by Don Kiely about one of the biggest buzzwords of this moment: SOA, Ruby on Rails is the other of course.

Here is an excerpt from the introduction: "The dominant client-server and n-tier application architectures of the 1990s ran into serious scalability and availability issues when used to implement massive Internet e-commerce sites. One of the major problems is that data tended to be stored in a massive, centralized database that all client components had direct access to. Virtually all communication with the database was in the form of SQL statements or batches of statements in a stored procedure, so that the client received a set of data for the specific task at hand.

Other problems arose when trying to incorporate “legacy” systems into newer applications. After decades of deploying a wide variety of systems using various proprietary technologies and platforms, the world was awash in systems that did their job perfectly well but had no clear path to interact with other applications in an increasingly connected environment. Achieving the agility needed by today’s applications has been extremely difficult. Business-to-business (B2B) interactions complicate things even further, requiring standard and reliable ways of conducting business electronically. Clearly, evolving systems that meet the needs of today’s global"

Read the complete white paper here: How SQL Server 2005 Enables Service-Oriented Database Architectures

Friday, September 01, 2006

SQL Server 2005 Best Practices Analyzer Coming Soon??

Microsoft Events has the following TechNet Webcast: Using the SQL Server Upgrade Advisor and New SQL Server 2005 Best Practices Analyzer Tools (Level 200)

Start Time: Thursday, September 07, 2006 9:30 AM Pacific Time (US & Canada)
End Time: Thursday, September 07, 2006 11:00 AM Pacific Time (US & Canada)


Description: Do you have plans to upgrade to Microsoft SQL Server 2005 in the near future? In this presentation, we describe two valuable tools from Microsoft that can help you identify and address potential issues proactively for a smoother upgrade experience. The Microsoft SQL Server 2005 Upgrade Advisor analyzes existing instances of Microsoft SQL Server 7.0 and SQL Server 2000, identifies feature and configuration changes that might affect your upgrade, and provides links to documentation that describes each issue and how to resolve it. The new SQL Server 2005 Best Practices Analyzer tool helps you ensure that SQL Server instances, databases, and SQL Server Integration Services (SSIS) packages adhere to Microsoft best practices. Attend this webcast to learn how to use these tools and how they can help you upgrade your SQL Server environment effectively and efficiently.

Presenter: Paul Mestemaker, Program Manager, Microsoft Corporation


So does this mean that the SQL Server 2005 Best Practices Analyzer is near completion? I don't know but I did ask the same question on the SQL Server Relational Engine Manageability Team Blog


And to give credit where credit is due I saw this first on Dis4ea's SQL Blog

Top SQL Server Google Searches For August 2006

These are the top SQL Searches on this site for the month of August I have left out searches that have nothing to do with SQL Server or programming (for example atlantic city escorts)

Here are the results...
dtsrun from sp
query multiple databases
first business day of each month query
Truncated table recovery
check constraint
dbcc report files
first business day of each month
String or binary data would be truncated.
SQL SELECT *
substr()
Login failed for user '(null)'. Reason: Not associated with a trusted SQL Server connection.
xp_fileexist
SQL SELECT WHERE DATE
CONCAT_NULL_YIELDS_NULL
check constrant
SQL 2000 parallel backup restore
dtsrun

Let's talk about a couple of these

query multiple databases
I covered that in this post

first business day of each month query
You really need to have a calendar table for this one. You can also use a number table and check for the min date where select datepart(dw,date) between 2 and 6 but what about holidays. A calendar table is your best bet. And I know just a place to get some code for that-->A way to load a calendar table

Login failed for user '(null)'. Reason: Not associated with a trusted SQL Server connection.
That can be found here: 2000 version, 2005 version

xp_fileexist
That is covered here

String or binary data would be truncated
And that was covered here


So there you have it, those were some of the searches and I covered some of that stuff already. I always like to look at the searches because it gives me ideas for future blog posts

Top 5 Posts For The Month Of August

Below are the top 5 posts according to Google Analytics for the month of August

Here are the posts in order by pageviews descending

Store The Output Of A Stored Procedure In A Table Without Creating A Table
6 Different Ways To Get The Current Identity Value From A Table
COALESCE And ISNULL Differences
Login failed for user 'sa'. Reason: Not associated with a trusted SQL Server connection. SQL 2005
OPENROWSET And Excel Problems

And I have also updated the Top 10 Articles of all time