all these while i've only used varchar for any string
i heard from my ex-boss that char helps speed up searches. is that
true?
so there are these:
1) char with index
2) char without index
3) char with clustered index
4) varchar with index
5) varchar without index
6) varchar with clustered index
some of my tables primary key (clustered) is a string type. would it
be benificial to use char? or would using (6) makes no difference?
for non primary key columns that needs to be searched a lot, can i say
(1) is the best? 4 8861
oh and
if the column is char(10)
and there's this data 'abc '
so is there a difference between these two ?
select * from t1 where col = 'abc'
or
select * from t1 where col='abc '
Nick Chan (zz*******@yaho o.com) writes:
all these while i've only used varchar for any string
i heard from my ex-boss that char helps speed up searches. is that
true?
so there are these:
1) char with index
2) char without index
3) char with clustered index
4) varchar with index
5) varchar without index
6) varchar with clustered index
some of my tables primary key (clustered) is a string type. would it
be benificial to use char? or would using (6) makes no difference?
The choice between char and varchar should be made be from the business
rules. If I see a char(12) column, I expect most columns to have 12
characters without trailing blanks.
I can't see why char would things faster. The physical layout of the row
is somewhat simpler, but on the other hand if the average length is far
from the max length, the char columns takes up more space, and more
space means more pages to read, and thus longer access times.
if the column is char(10)
and there's this data 'abc '
so is there a difference between these two ?
select * from t1 where col = 'abc'
or
select * from t1 where col='abc '
Why don't you test? I think they are the same, as trailing blanks are
ignore when comparing. But these two are not the same:
SELECT * FROM tbl WHERE col LIKE @varcharval + '%'
SELECT * FROM tbl WHERE col LIKE @charval + '%'
--
Erland Sommarskog, SQL Server MVP, es****@sommarsk og.se
Books Online for SQL Server 2005 at http://www.microsoft.com/technet/pro...ads/books.mspx
Books Online for SQL Server 2000 at http://www.microsoft.com/sql/prodinf...ons/books.mspx
Nick Chan wrote:
>
all these while i've only used varchar for any string
i heard from my ex-boss that char helps speed up searches. is that
true?
so there are these:
1) char with index
2) char without index
3) char with clustered index
4) varchar with index
5) varchar without index
6) varchar with clustered index
some of my tables primary key (clustered) is a string type. would it
be benificial to use char? or would using (6) makes no difference?
for non primary key columns that needs to be searched a lot, can i say
(1) is the best?
I don't think there is a big performance difference between
handling/comparing a char column versus a varchar column.
So for optimal performance, it comes down to two other aspects, required
space and fragmentation.
A varchar has an overhead of 2 bytes per values. These 2 bytes specify
the length of the value. Also, if the column in question is the only
varchar column in the table, then you should add another byte (because
that byte would be saved if no varchar columns were used). So then,
based on the average value length, you can calculate whether char or
varchar uses the least space. For example, a varchar(10) with an average
data length of 6 would require less space than a char(10). Another
example: a varchar(2) will always be less space efficient than a
char(2).
The other consideration is fragmentation. If you use a varchar column,
and it is updated often, and the updates will often change the data
length of the value, then this will cause fragmentation. Updates of a
char column can always be done in place, which minimizes fragmentation.
So in general, if the column's defined size is small, or if the average
data length is close to the defined length, then you best choose char,
otherwise, use varchar.
--
Gert-Jan
Thanks guys for the replies !!
On Sep 8, 3:48 am, Gert-Jan Strik <so...@toomuchs pamalready.nlwr ote:
Nick Chan wrote:
all these while i've only used varchar for any string
i heard from my ex-boss that char helps speed up searches. is that
true?
so there are these:
1) char with index
2) char without index
3) char with clustered index
4) varchar with index
5) varchar without index
6) varchar with clustered index
some of my tables primary key (clustered) is a string type. would it
be benificial to use char? or would using (6) makes no difference?
for non primary key columns that needs to be searched a lot, can i say
(1) is the best?
I don't think there is a big performance difference between
handling/comparing a char column versus a varchar column.
So for optimal performance, it comes down to two other aspects, required
space and fragmentation.
A varchar has an overhead of 2 bytes per values. These 2 bytes specify
the length of the value. Also, if the column in question is the only
varchar column in the table, then you should add another byte (because
that byte would be saved if no varchar columns were used). So then,
based on the average value length, you can calculate whether char or
varchar uses the least space. For example, a varchar(10) with an average
data length of 6 would require less space than a char(10). Another
example: a varchar(2) will always be less space efficient than a
char(2).
The other consideration is fragmentation. If you use a varchar column,
and it is updated often, and the updates will often change the data
length of the value, then this will cause fragmentation. Updates of a
char column can always be done in place, which minimizes fragmentation.
So in general, if the column's defined size is small, or if the average
data length is close to the defined length, then you best choose char,
otherwise, use varchar.
--
Gert-Jan- Hide quoted text -
- Show quoted text -
This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: dmhendricks |
last post by:
Greetings,
I have a question. I work on some SQL2k/ASP.NET apps at work. My
predacessor, who created the databases/tables seemed to have liked to
use 'char' for all text fields. Is there a reason why he would have
done this over using varchar? It's a minor annoyance to always have to
RTRIM data and it makes directly making changes to the database more
annoying (with all the pointless trailing spaces)?
I usually use char for fixed...
|
by: twkelsey |
last post by:
Hi,
My company has a scenario where we would like to change the data type
of an existing primary key from an integer to a char, but we are
concerned about the performance implications of doing so. The script
for the two tables that we need to modify is listed below. Table
FR_Sessions contains a column named TransmissionID which is currently
an integer. This table contains about 1 million rows of data. Table
FR_VTracking table also...
|
by: jim_geissman |
last post by:
One table I manage has a clustered index, and it includes some
varchar columns. When it is initially created, all the columns
in the clustered index are populated, and then some of the longer
varchars are populated through update queries. If the varchar
columns are stored outside the clustered structure, then it would
make sense to create the clustered index before populating the
varchar columns. Otherwise it would make sense to wait,...
|
by: Techie |
last post by:
what's the difference of the two data types?
|
by: jdokos |
last post by:
Hello,
I have a question about VARCHAR fields. Our application groups here
are starting to use VARCHARs much more frequently. Even VARCHAR (2) to
(9) length fields. They say this is because some of the application
programs, specifically Java Beans cannot handle the spaces after the
value in CHAR fields.
Is anyone else seeing this trend?
| |
by: Troels Arvin |
last post by:
Hello,
In the DBMS I know best, PostgreSQL, there is no real performance
difference between CHAR and VARCHAR. And since CHAR pads with spaces, I
generally dislike CHAR (with CHAR, it's not possible to see if the input
value had trailing spaces or not, for example).
How is it in DB2?
More specifically: If a column has type CHAR(20) and most of the strings
|
by: D. |
last post by:
Hi,
I'm planning the structure of a SqlServer 2005 database for a new
application.
The requirement is that primary keys must be "natural"; i.e. in the table
Customers the primary key will be a max. 10 characters string (but the
string may be filled i.e. with only 5 charachters).
Should I define these primary keys as char or varchar?
I'm interested in your opinion in particular about performace issue, because
there will be tables with...
|
by: Medhatithi |
last post by:
I have a table whose indexed column is a char(16) field. I am giving the schema.
CREATE TABLE Emp(Empno char(16),
Ename varchar(25),
Salary number(10,2),......)
Now, there is an index on the Empno field. Now, inside a stored procedure, I am executing a statement
select Name=Ename from Emp where Empno=@eno
This @eno is varchar(25). So, SQL Server would do the implicit...
|
by: maheshmohta |
last post by:
Background
Often while remodeling legacy application, one of the important tasks for the architects is to have an optimum usage of storage capabilities of database. Most of the legacy applications are constrained by the technology available at the time of their development and hence aren’t optimum as per current scenario. One of such cases is the extensive usage of CHAR fields, which aren’t optimum solution for space storage now. This paper...
|
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it.
First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
|
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed.
This is as boiled down as I can make it.
Here is my compilation command:
g++-12 -std=c++20 -Wnarrowing bit_field.cpp
Here is the code in...
| |
by: jinu1996 |
last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth.
The Art of Business Website Design
Your website is...
|
by: Hystou |
last post by:
Overview:
Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
|
by: tracyyun |
last post by:
Dear forum friends,
With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the choice of these technologies. I'm particularly interested in Zigbee because I've heard it does some...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
|
by: conductexam |
last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one.
At the time of converting from word file to html my equations which are in the word document file was convert into image.
Globals.ThisAddIn.Application.ActiveDocument.Select();...
|
by: adsilva |
last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
| |
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| |