Like:
insert into table (col) values (N'multilingual unicode strings')
I'm using SQL Server 2008 and I already use nVarChar as the column data type.
You need the N'' syntax only if the string contains characters which are not inside the default code page. "Best practice" is to have N'' whenever you insert into an nvarchar or ntext column.
Yes, you do if you have unicode characters in the strings.
From books online (http://msdn.microsoft.com/en-us/library/ms191313.aspx)...
"Unicode string constants that appear in code executed on the server, such as in stored procedures and triggers, must be preceded by the capital letter N. This is true even if the column being referenced is already defined as Unicode. Without the N prefix, the string is converted to the default code page of the database. This may not recognize certain characters. The requirement to use the N prefix applies to both string constants that originate on the server and those sent from the client."
It is preferable for compatibility sake.
Best practice is to use parameterisation in which case you don't need the N prefix.
Related
I have seen prefix N in some insert T-SQL queries. Many people have used N before inserting the value in a table.
I searched, but I was not able to understand what is the purpose of including the N before inserting any strings into the table.
INSERT INTO Personnel.Employees
VALUES(N'29730', N'Philippe', N'Horsford', 20.05, 1),
What purpose does this 'N' prefix serve, and when should it be used?
It's declaring the string as nvarchar data type, rather than varchar
You may have seen Transact-SQL code that passes strings around using
an N prefix. This denotes that the subsequent string is in Unicode
(the N actually stands for National language character set). Which
means that you are passing an NCHAR, NVARCHAR or NTEXT value, as
opposed to CHAR, VARCHAR or TEXT.
To quote from Microsoft:
Prefix Unicode character string constants with the letter N. Without
the N prefix, the string is converted to the default code page of the
database. This default code page may not recognize certain characters.
If you want to know the difference between these two data types, see this SO post:
What is the difference between varchar and nvarchar?
Let me tell you an annoying thing that happened with the N' prefix - I wasn't able to fix it for two days.
My database collation is SQL_Latin1_General_CP1_CI_AS.
It has a table with a column called MyCol1. It is an Nvarchar
This query fails to match Exact Value That Exists.
SELECT TOP 1 * FROM myTable1 WHERE MyCol1 = 'ESKİ'
// 0 result
using prefix N'' fixes it
SELECT TOP 1 * FROM myTable1 WHERE MyCol1 = N'ESKİ'
// 1 result - found!!!!
Why? Because latin1_general doesn't have big dotted İ that's why it fails I suppose.
1. Performance:
Assume your where clause is like this:
WHERE NAME='JON'
If the NAME column is of any type other than nvarchar or nchar, then you should not specify the N prefix. However, if the NAME column is of type nvarchar or nchar, then if you do not specify the N prefix, then 'JON' is treated as non-unicode. This means the data type of NAME column and string 'JON' are different and so SQL Server implicitly converts one operand’s type to the other. If the SQL Server converts the literal’s type
to the column’s type then there is no issue, but if it does the other way then performance will get hurt because the column's index (if available) wont be used.
2. Character set:
If the column is of type nvarchar or nchar, then always use the prefix N while specifying the character string in the WHERE criteria/UPDATE/INSERT clause. If you do not do this and one of the characters in your string is unicode (like international characters - example - ā) then it will fail or suffer data corruption.
Assuming the value is nvarchar type for that only we are using N''
I have a table with columns that contain both thai and english text data. NVARCHAR(255).
In SSMS I can query the table and return all the rows easy enough. But if I then query specifically for one of the Thai results it returns no rows.
SELECT TOP 1000 [Province]
,[District]
,[SubDistrict]
,[Branch ]
FROM [THDocuworldRego].[dbo].[allDistricsBranches]
Returns
Province District SubDistrict Branch
อุตรดิตถ์ ลับแล ศรีพนมมาศ Northern
Bangkok Khlong Toei Khlong Tan SSS1
But this query:
SELECT [Province]
,[District]
,[SubDistrict]
,[Branch ]
FROM [THDocuworldRego].[dbo].[allDistricsBranches]
where [Province] LIKE 'อุตรดิตถ์'
Returns no rows.
What do I need o do to get the expected results.
The collation set is Latin1_General_CI_AS.
The data is displayed and inserted with no errors just can't search.
Two problems:
The string being passed into the LIKE clause is VARCHAR due to not being prefixed with a capital "N". For example:
SELECT 'อุตรดิตถ์' AS [VARCHAR], N'อุตรดิตถ์' AS [NVARCHAR]
-- ????????? อุตรดิตถ
What is happening here is that when SQL Server is parsing the query batch, it needs to determine the exact type and value of all literals / constants. So it figures out that 12 is an INT and 12.0 is a NUMERIC, etc. It knows that N'ดิ' is NVARCHAR, which is an all-inclusive character set, so it takes the value as is. BUT, as noted before, 'ดิ' is VARCHAR, which is an 8-bit encoding, which means that the character set is controlled by a Code Page. For string literals and variables / parameters, the Code Page used for VARCHAR data is the Database's default Collation. If there are characters in the string that are not available on the Code Page used by the Database's default Collation, they are either converted to a "best fit" mapping, if such a mapping exists, else they become the default replacement character: ?.
Technically speaking, since the Database's default Collation controls string literals (and variables), and since there is a Code Page for "Thai" (available in Windows Collations), then it would be possible to have a VARCHAR string containing Thai characters (meaning: 'ดิ', without the "N" prefix, would work). But that would require changing the Database's default Collation, and that is A LOT more work than simply prefixing the string literal with "N".
For an in-depth look at this behavior, please see my two-part series:
Which Collation is Used to Convert NVARCHAR to VARCHAR in a WHERE Condition? (Part A of 2: “Duck”)
Which Collation is Used to Convert NVARCHAR to VARCHAR in a WHERE Condition? (Part B of 2: “Rabbit”)
You need to add the wildcard characters to both ends:
N'%อุตรดิตถ์%'
The end result will look like:
WHERE [Province] LIKE N'%อุตรดิตถ์%'
EDIT:
I just edited the question to format the "results" to be more readable. It now appears that the following might also work (since no wildcards are being used in the LIKE predicate in the question):
WHERE [Province] = N'อุตรดิตถ์'
EDIT 2:
A string (i.e. something inside of single-quotes) is VARCHAR if there is no "N" prefixed to the string literal. It doesn't matter what the destination datatype is (e.g. an NVARCHAR(255) column). The issue here is the datatype of the source data, and that source is a string literal. And unlike a string in .NET, SQL Server handles 'string' as an 8-bit encoding (VARCHAR; ASCII values 0 - 127 same across all Code Pages, Extended ASCII values 128 - 255 determined by the Code Page, and potentially 2-byte sequences for Double-Byte Character Sets) and N'string' as UTF-16 Little Endian (NVARCHAR; Unicode character set, 2-byte sequences for BMP characters 0 - 65535, two 2-byte sequences for Code Points above 65535). Using 'string' is the same as passing in a VARCHAR variable. For example:
DECLARE #ASCII VARCHAR(20);
SET #ASCII = N'อุตรดิตถ์';
SELECT #ASCII AS [ImplicitlyConverted]
-- ?????????
Could be a number of things!
Fist of print out the value of the column and your query string in hex.
SELECT convert(varbinary(20)Province) as stored convert(varbinary(20),'อุตรดิตถ์') as query from allDistricsBranches;
This should give you some insight to the problem. I think the most likely cause is the ั, ิ, characters being typed in the wrong sequence. They are displayed as part of the main letter but are stored internally as separate characters.
Any idea why the Turkish Lira symbol is replaced by a question mark when I insert it in a table in the database. See the image below
This is not a font issue. This is a Unicode (UTF-16) vs 8-bit Code Page character set issue (i.e. NVARCHAR vs VARCHAR). The character you are trying to use does not exist in the particular Code Page indicated by the default Collation of the DB in which you are executing this query. The Code Page used by the DB's default Collation is relevant here since your string literal is not prefixed with an upper-case "N". If it was, then the string would be interpreted as being Unicode and no conversion would take place. But since you are passing in a non-Unicode string, it will be forced into the current DB's default Collation's Code Page as the query is parsed. Any characters not available in that Code Page, and not having a Best-fit mapping, get turned into "?".
You can run the following to see for yourself:
SELECT '₺';
PRINT '₺';
It both prints AND displays in the results grid as ?
If you want to see what character SQL Server thinks it is, run the following:
SELECT ASCII('₺');
And it will return: 63
If you want to see what character has an ASCII value of 63, run this:
SELECT CHAR(63);
And it will return: ?
Now run this:
SELECT N'₺';
PRINT N'₺';
This will both print and display in the results grid correctly.
To see what character value the symbol really is, run the following:
SELECT UNICODE(N'₺'), UNICODE('₺');
This will return: 8378 and 63
But isn't 63 the question mark? Yes. That is because not prefixing the string literal '₺' with a capital "N" tells SQL Server that it is VARCHAR and so it gets translated to the default unknown character.
Now, if you were to execute this VARCHAR version in a DB that had a Collation tied to a Code Page that had this character, then it would work even when not prefixing the string literal with an upper-case "N". However, at the moment, I cannot find any Code Page used within SQL Server that supports this character. So, it might be a Unicode-only character, at least at far as SQL Server is concerned.
The way to fix this is:
Change the datatype of the field to NVARCHAR (I see in a comment on the question that the field is currently VARCHAR). If the field is VARCHAR then even if you use the N prefix on the string, the character will still get stored as ?, unless the Code Page specified by the Collation of the column supports this character, but again, I think this might be a Unicode-only character.
Change your INSERT statement to prefix the string field with a capital "N": (73, 4, N'(3) ₺'). Even if you change the field to NVARCHAR, if you don't prefix the string with N then SQL Server will translate the character to ? first and then insert the ?. This is because the query gets parsed before it gets executed, and parsing (for non-Unicode string literals and variables) is done in the Code Page of the DB's default Collation
Probably for the same reason my browser isn't displaying it in the title for this question: It isn't in the application's character set (or maybe not supported by the font).
In this case, my browser shows some numbers in a box (denoting the character code).
SQL-server is translating it to a known character instead.
Ensure you're storing it in a field that supports the character in it's character set (I think UTF-8 is sufficient)
Dear Friends,
I've faced with a problem never thought of ever. My problem seems too simple but I can't find a solution to it.
I have a sql server database column that is of type NVarchar and is filled with standard persian characters. when I'm trying to run a very simple query on it which incorporates the LIKE operator, the resultset becomes empty although I know the query term is present in the table. Here is the very smiple example query which doesn't act corectly:
SELECT * FROM T_Contacts WHERE C_ContactName LIKE '%ف%'
ف is a persian character and the ContactName coulmn contains multiple entries which contain that character.
Please tell me how should I rewrite the expression or what change should I apply. Note that my database's collation is SQL_Latin1_General_CP1_CI_AS.
Thank you very much
Also, if those values are stored as NVARCHAR (which I hope they are!!), you should always use the N'..' prefix for any string literals to make sure you don't get any unwanted conversions back to non-Unicode VARCHAR.
So you should be searching:
SELECT * FROM T_Contacts
WHERE C_ContactName COLLATE Persian_100_CI_AS LIKE N'%ف%'
Shouldn't it be:
SELECT * FROM T_Contacts WHERE C_ContactName LIKE N'%ف%'
ie, with the N in front of the comparing string, so it treats it like an nvarchar?
USE AdventureWorks;
GO
IF OBJECT_ID (N'dbo.AWBuildVersion', N'U') IS NOT NULL
DROP TABLE dbo.AWBuildVersion;
GO
Whats the N symbolize in N'dbo.AWBuildVersion' & N'U' ?
It's for Unicode. It's like an nvarchar or nchar SQL data type.
For more information, see this: You must precede all Unicode strings with a prefix N when you deal with Unicode string constants in SQL Server
This StackOverflow article has info on the subject. Basically the 'N' prefix denotes a Unicode string.
When dealing with Unicode string constants in SQL Server you must precede all Unicode strings with a capital letter N.
The "N" prefix stands for National Language in the SQL-92 standard, and must be uppercase.
If you do not prefix a Unicode string constant with N, SQL Server will convert it to the non-Unicode code page of the current db before it uses the string.
Sometimes people use N' out of habit, not when it is really necessary.