Does it really take twice as much space to store at all times? Unicode is only 16-bits wide when using characters outside of the standard 7-bit ASCII range. If you are primarily storing English, wouldn't the nvarchar therefore only store most characters as 8-bit wide as well? That's how unicode works in most programming languages... Just curious, I have no idea how SQL works in this respect.
Actually, most programming languages use two bytes (the equivalent of a WCHAR instead of a CHAR) to store unicode character data, regardless of what the data contains. It would be a lot of overhead to try to determine, at runtime, whether each character could safely be chopped down to a single byte; so either you've declared up front that you're going to allocate space for unicode throughout the string, or you've declared that you won't.
This the best example of a man of few words.
Excellent way to explain.
Just a note:
IIRC, Java uses unicode internally for strings throughout anyway, and has to convert to 8-bit on the fly.
UCS-2 is typical for in-memory representation and UTF-8 for serialisation.
NVARCHAR is UCS-2.
Very Useful Explanation in few words...............
thanx Adam
Adam thanks ,Its Really good information.
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If you have any plans to store accented characters and the like, nvarchar is definitely the way to go. It avoids all the problems which different character sets and code pages can introduce.
Strangely, though, you are still expected to define a collating sequence for such a column, which is very much an 8-bit-character kind of thing. Can anyone throw any light on this?
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"Strangely, though, you are still expected to define a collating sequence for such a column"
Well, I don't work for Microsoft so I can't say that I know why they did it.
But I may have a clue though. If you set up your column to accept unicode data, it's basically because you expect accents or other special characters.
From a language to another, the way those characters are sorted (does the e acute comes after Z, as in English, or after E, as in French?) changes. So it makes sense to give an hint to the DB enigne as to what to do with the data.
It think that it's like telling the DB : "Okay, this is unicode, but you should threat it like a Greek would do".
That's what I think it is, anyway... :)
Thank you for putting this up, its simple and to the point.
Just the information I was looking for! Thanks!
Aha that's what they are! Excellent info !
Perfect answers! Sheesh you guys are smart!
Thanks for complete information
Thanks for the simple answer to a simple question.
I believe SQL server is optimized for unicode data so the question becomes is there really a benefit to using varchar over nvarchar outside of disk space? Does SQL Server convert UTF-8 to an internal unicode format before working with it? I know quite a few other areas of Microsoft software do this unless you specify not to.
then varchar also sufficint right..it is also used for dynamic thing only....if i ll give like varchar(max) then nothing difference right?
i got information about varchar in this area...
nvarchar should always be used, otherwise you end up with code page conversion issues and lots of pain.
Thanks. That's what i am looking for
How come I am able to store a unicode character in a varchar field?
Jesse, I have the same question. My field is varchar, but I can store there characters as ššžýá. But I am not able to save another national characters -e.g. čř. This can be done only with nvarchar.
Maybe collation setting on the database infuece it, too.
@Jesse, Petra
Those special characters are still ASCII characters, so you can store them in a varchar column.
Here's a link to the entire ASCII set
www.codetoad.com/.../ascii_characters.asp
varchar is good for English, Spanish, German, French and many other European languages.
You'll need nvarchar for languages like Japanese, Korean, Hindi and Arabic that aren't descendents of Latin languages.
thanks, i had a problem with the database size, now i solved it...
I ran into an issue of incredibly poor performance with 'linking' varchar and nvarchar fields in supposing they were practically identical... but it went away completely (going from a 10 minute query down to 6 seconds) when I made both table fields identical type - at varchar.
sp_executesql (please don't hurt me for mentioning prepared sql)... requires nvarchar for @stmt parameter... up to nvarchar(max) in 2005 or nvarchar(4000) in 2000. Correct me if I'm wrong. -Cal
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I have programmed spanish/english applications for several years and I have always used varchar for the string fields. I have never had an issue with them. Spanish accented characters and tildes (ñ) are stored and retrieved with no problem at all.
I have read just what Randall said above: nvarchar (unicode) fields are necessary when you have the need to store japanese, chinese or other "strange" characters.
I saw what you guys wrote above, but I am still not sure of how nvarchar affects performance.
Lets say I have in my mssql only few tables with columns that may have Latin characters, how will the performance be affected if I change these specific columns to be nvarchar?
Ora,
Not sure about that, but in the original post you can read,
"...The reason for this is that nvarchar takes twice as much space as varchar..."
If you have lots of data, that can be a problem.
I can't see another performance problem
This is the "Feeling Lucky" hit for "varchar vs nvarchar" :)
Thank you very much for sharing this information
Yes, It really takes twice as much space at all times. The reason you declare how long a varchar or nvarchar is so that the Database App can reserve a specified amount of space for that variable. If you have a field set up as varchar(15) and your data is only 3 characters long, it will still take up 15 characters of storage because that is how much space the Database App reserved.
Short and sweet dude. Took me longer to write this comment than to get my answer.
Since data-storage is not the problem anymore, I allways use nvarchar.
Space may not be a problem these days, however I typically see the bigger the database the longer it may take to perform IO intensive queries.
Of course 1/2 the field size dosent mean 2x the query speed however what about when transmitting the data? espically over slower network.
Also why not use a user defined datatype, so if you do need to change the type the task is a little easier.
I totally agree, If you don't need it shouldn't be using NVarchar as size of data increases, transmission time increses. Good Article
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What about conversion issues since ADO.NET uses Unicode and indexing etc. searching for varchar with an nvarchar parameter? Does that blow the indexing?
What Anthony said above about the query issue joining nvarchar to varchar is a known bug. I had the same issue and resolved by making both varchar.
Wouldn't nVarchars be slower in sorting, searching and joining because the processor has to look at twice as many bits to perform any action?
Honestly I don't see any difference in practical terms regarding the Portuguese language and the currency symbol €. Made a simple test with a table with 2 columns, one NVARCHAR and another VARCHAR. Insert text with characters such as é, â, ã, ç and € in both columns and it all seems the same. Didn't get any errors or warnings.
Even executing a select on the data seems OK.
I'm missing something?
Never the less good post and good explanation on NVARCHAR and VARCHAR differences.
Very explainatory and really good article.
I have one query...
If any one can help me to write an SP which
convert all the nvarchar data type to varchar datatypes in all tables in a database in SQL Server
Excellent short and sweet comparison
Exactly what I was looking for, cheers for the concise answer.
Guys, the bottom line is bits.
You have 8 bits to represent the English and European languages in ASCII character set (forget other language and symbol sets).
Once you need more, you have to go to Unicode...16 bits...like Japanese. I have done this coding before...delivered a Japanese Windows product...originally written in English.
Expect to store everything in SQL as an NCHAR or NVARCHAR column.
This is the safest way to go....and performance is not an issue unless you are storing huge text fields (which you shouldn't be using anyway).
Otherwise, your code is portable and internationalization-ready.
Sometimes it is best to ignore performance in exchange for other benefits (and simplicity). We have 64-bit Windows, multiple-core processors, fast hard drives, and unlimited virtual memory now.
Just my opinion. :)
Peace,
Scott
@ Jesse, Petra, Pablo, Joquim:
The characters you mention that work are single-byte characters that belong to the Windows-1252 codepage, all of which are stored as a single byte without issue.
Randall:
ASCII only defines 0x7F characters. From 0x80 to 0xFF are defined by some other codepage that is a superset of ASCII - most likely Windows-1252 or ISO-8859-1 (which only differ from each other for about 16 values, IIRC). Your link is actually showing one of these 256-character codepages, and calling it (incorrectly) ASCII.
This could start World War 3
This is best example Thanks
thanks for the nice and concise explanation. couldn't quite understand the difference between these two data types ever before.
wow! very useful blog. thanks
Thanks! This blog put things in black ans white
Somebody really read the entire blog?, I only read some comments and I lost the idea of the discussion.
Regards.
Switching everything to varchar. We use English and Spanish only. Thanks for all the comments.
"The reason for this is that nvarchar takes twice as much space as varchar"
You are correct for the most part, except for the size. The size of varchar in bytes is the length of text * 2. The size of nvarchar is the length of text * 2 + 2 bytes. As you can see, nvarchar only adds an additional two bytes, but is still worth considering for large databases.
The above statement is only true if the string is a single character, because for a single byte to be stored as varchar, you need to multiply by two so:
Varchar = “a”
Bytes = 1*2 = 2
Nvarchar = “a”
Bytes = 1 * 2 + 2 = 4
Now assuming you have 5 letters:
Varchar = “abcde”
Bytes = 5 * 2 = 10
Nvarchar = “abcde”
Bytes = 5 * 2 + 2 = 12
Reference:
msdn.microsoft.com/.../ms186939.aspx
No, NVARCHAR will be twice as big (almost) as VARCHAR and NO, unlike someone said earlier, VARCHAR/NVARCHAR DO NOT reserve the full space size, that's the difference between a char and a varchar.
A varchar includes 2 size bytes and then the data, so to store 20 characters in a varchar(100) would take 20 bytes + 2 bytes for the length, so 22 bytes.
An nvarchar also includes a size indicator but takes 2 bytes per character. So 20 characters would be stores as (20 * 2) bytes + 2 bytes for the length, so 42 bytes.
CHAR and NCHAR preallocated the space so a CHAR(20) will always take 20 bytes even if value stores is only 1 character. An NCHAR(20) would take 40 bytes.
The advantage of CHAR/NCHAR is when retrieving data, no logic has to be used to determine how much data is stored, since size is fixed, making some operations faster. That's why it is recommended when the size of the data varies little and will almost always be the size of the field, like a field for storing state abbreviations, CHAR(2) and your done.
You use VARCHAR/NVARCHAR when the size of the data stored varies, like names and descriptions.
msdn.microsoft.com/.../ms176089.aspx
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Great info.
Is Join on nvarchar and varchar is still an issue with MS SQL 2008?
Ha sany one tried it?
Thanks, that's what i'm looking for
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Thanks for this! Now I have to cringe over how many times over the last decade I used nvarchar stupidly and wasted all that memory. *cringe*
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What about symbols (aka English - nothing special) but you need to display the Degree symbol for Farenheit (aka deg F using symbol). I believe that requires the usage of NVARCHAR over VARCHAR.
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Hmm, another consideration is that the OS converts from code page to Unicode before collating, so varchar should be slower....
I also run into problems all the time from customers that have had their markets grow or suddenly start otherwise seeing "unexpected" data that's now suddenly important that they hadn't planned for.
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