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''
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 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've read all about varchar versus nvarchar. But I didn't see an answer to what I think is a simple question. How do you determine the length of your nvarchar column? For varchar it's very simple: my Description, for example, can have 100 characters, so I define varchar(100). Now I'm told we need to internationalize and support any language. Does this mean I need to change my Description column to nvarchar(200), i.e. simply double the length? (And I'm ignoring all the other issues that are involved with internationalization for the moment.)
Is it that simple?
Generally it is the same as for varchar really. The number is still the maximum number of characters not the data length.
nvarchar(100) allows 100 characters (which would potentially consume 200 bytes in SQL Server).
You might want to allow for the fact that different cultures may take more characters to express the same thing though.
An exception to this is however is if you are using an SC collation (which supports supplementary characters). In that case a single character can potentially take up to 4 bytes.
So worst case would be to double the character value declared.
From microsoft web site:
A common misconception is to think that NCHAR(n) and NVARCHAR(n), the n defines the number of characters. But in NCHAR(n) and NVARCHAR(n) the n defines the string length in byte-pairs (0-4,000). n never defines numbers of characters that can be stored. This is similar to the definition of CHAR(n) and VARCHAR(n).
The misconception happens because when using characters defined in the Unicode range 0-65,535, one character can be stored per each byte-pair. However, in higher Unicode ranges (65,536-1,114,111) one character may use two byte-pairs. For example, in a column defined as NCHAR(10), the Database Engine can store 10 characters that use one byte-pair (Unicode range 0-65,535), but less than 10 characters when using two byte-pairs (Unicode range 65,536-1,114,111). For more information about Unicode storage and character ranges, see
https://learn.microsoft.com/en-us/sql/t-sql/data-types/nchar-and-nvarchar-transact-sql?view=sql-server-ver15
#Musa Calgar - exactly right. That link has the information for the answer to this question.
But to make sure the question itself is clear, we are talking about the 'length' attribute we see when we look at the column definition for a given table, right? That is the storage allocated per column. On the other hand, if we want to know the number of characters for a given string in the table at a given moment you can:
"SELECT myColumn, LEN(myColumn) FROM myTable"
But if the storage length is desired, you can drag the table name into the query window using SSMS, highlight it, and use 'Alt-F1' to see the defined lengths of each column.
So as an example, I created a table like this specifiying collations. (Latin1_General_100_CI_AS_SC allows for supplemental characters - that is, characters that take more than just 2 bytes):
CREATE TABLE [dbo].[TestTable1](
[col1] [varchar](10) COLLATE Latin1_General_100_CI_AS,
[col2] [nvarchar](10) COLLATE Latin1_General_100_CI_AS_SC,
[col3] [nvarchar](10) COLLATE Latin1_General_100_CI_AS
) ON [PRIMARY]
The lengths show up like this (Highlight in query window and Alt-F1):
Column_Name Type Length [...] Collation
col1 varchar 10 Latin1_General_100_CI_AS
col2 nvarchar 20 Latin1_General_100_CI_AS_SC
col3 nvarchar 20 Latin1_General_100_CI_AS
If you insert ASCII characters into the varchar and nvarchar fields, it will allow you to put 10 characters into all of them. There will be an error if you try to put more than 10 characters into those fields:
"String or binary data would be truncated.
The statement has been terminated."
If you insert non-ASCII characters like 'ā' you can still put 10 of them into each one, but SQL Server will convert the values going into col1 to the closest known character that fits into 1-byte. In this case, 'ā' will be converted to 'a'.
However, if you insert characters that require 4 bytes to store, like for example, '𠜎', you will only be allowed to put FIVE of them into the varchar and nvarchar fields. Any more than that will result in the truncation error shown above. The varchar field will show question marks because it has no single-byte character that it can convert that input to.
So when you insert five of these '𠜎', do a select of that row using len(<colname>) and you will see this:
col1 len(col1) col2 len(col2) col3 len(col3)
?????????? 10 𠜎𠜎𠜎𠜎𠜎 5 𠜎𠜎𠜎𠜎𠜎 10
So the length of col2 shows 5 characters since supplemental characters were defined when the table was created (see above CREATE TABLE DDL statement). However, col3 did not have _SC for its collation, so it is showing length 10 for the five characters we inserted.
Note that col1 has ten question marks. If we had defined the col1 varchar using the _SC collation instead of the non-supplemental one, it would behave the same way.
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 am using Sql Server 2008 R2 Enterprise. I am coding an application capable of inserting, updating, deleting and selecting records from a Sql tables. The application is making errors when it comes to the records that contain special characters such as ć, č š, đ and ž.
Here's what happens:
The command:
INSERT INTO Account (Name, Person)
VALUES ('Boris Borenović', 'True')
WHERE Id = '1'
inserts a new record but the Name field is Boris Borenovic, so character ć is changed to c.
The command:
SELECT * FROM Account
WHERE Name = 'Boris Borenović'
returns the correct record, so again the character ć is replaced by c and the record is returned.
Questions:
Is it possible to make Sql Server save the ć and other special characters mentioned earlier?
Is it still possible, if the previous question is resolved, to make Sql be able to return the Boris Borenović record even if the query asks for Boris Borenovic?
So, when saving records I want Sql to save exactly what is given, but when retrieving the records, I want it to be able to ingnore the special characters. Thanks for all the help.
1) Make sure the column is of type nvarchar rather than varchar (or nchar for char)
2) Use N' at the start of string literals containing such strings, e.g. N'Boris Borenović'
3) If you're using a client library (e.g. ADO.Net), it should handle Unicode text, so long as, again, the parameters are marked as being nvarchar/nchar instead of varchar/char
4) If you want to query and ignore accents, then you can add a COLLATE clause to your select. E.g.:
SELECT * FROM Account
WHERE Name = 'Boris Borenovic' COLLATE Latin1_General_CI_AI
Where _CI_AI means Case Insensitive, Accent Insensitive, should return all rows with all variants of the "c" at the end.
5) If the column in the table is part of a UNIQUE/PK constraint, and you need it to contain both "Boris Borenović" and "Boris Borenovic", then add a COLLATE clause to the column definition, but this time use a collation with "_AS" at the end, which says that it's accent sensitive.
To allow SQL Server to store special characters, use nvarchar instead of varchar for the column type.
When retrieving, you can force a accent-insensitve collation so that it ignores the different C's:
WHERE Name = 'Boris Borenović' COLLATE Cyrillic_General_CI_AI
Here, CI stands for Case Insensitive, and AS for Accent Insensitive.
I've faced with the same problem and after some researching:
https://dba.stackexchange.com/questions/139551/how-do-i-set-a-sql-server-unicode-nvarchar-string-to-an-emoji-or-supplementary
What is the difference between varchar and nvarchar?
I altered type of needed fields:
ALTER TABLE [table_name] ALTER COLUMN column_name [nvarchar]
GO
And it works!