I used to learn about SQL, especially MySQL. Then now my job requires me to understand Microsoft SQL Server (mssql). So I make these notes to guide me and others who want to transition to mssql. I usually summarized what I found and understood so far from browsing the internet.

My takeaways:

• It's declaring the string as  NCHAR,  NVARCHAR, or  NTEXT data type, rather than  CHAR,  VARCHAR, or  TEXT.

• This  N prefix denotes that subsequent string is in  Unicode (the N actually stands for National language character set).

• To quote from Microsoft:

  Without the N prefix, the string is converted to  the default code page of the database and  may not recognize certain characters.

• The  NVARCHAR column can store any Unicode data. The  VARCHAR column is restricted to an 8-bit.

• By using  NVARCHAR rather than  VARCHAR, we can  avoid doing encoding conversions every time we read from or write to the database. Some people think that  VARCHAR should be used because it takes up less space. Codepage incompatibilities are pain and Unicode is the cure for codepage problems.

• The  VARCHAR data type represents the  non-Unicode variable-length string data type. We can store letters, numbers, and special characters in it.

N represents  string size in bytes ( not a value representing the number of characters in a string).
It stores a  maximum of 8000 Non-Unicode characters.
It takes  1 byte per character. If we do not  explicitly specify the value for N, it takes  1-byte storage.

-- DECLARE @var AS VARCHAR(N) = 'text';DECLARE @text AS VARCHAR(100) = 'this VARCHAR yields 33 characters';SELECT
    @text AS Output,
    DATALENGTH(@text) AS Length;

The query above defines  VARCHAR data type with 100 bytes of data.

It returns the  string length as 33 because of 1 byte per character, including a space character.

• The  NVARCHAR data type is for the  Unicode variable-length character data type. We can store  both non-Unicode and Unicode characters (Japanese Kanji, Korean Hangul, etc.).

N represents  string size in bytes ( not a value representing the number of characters in a string).
It stores a  maximum of 4000 Unicode and Non-Unicode characters.
It takes  2 byte per character. If we do not  explicitly specify the value for N, it takes  2-byte storage.

-- DECLARE @var AS NVARCHAR(N) = N'text';DECLARE @text AS NVARCHAR(100) = N'this NVARCHAR yields 34 characters';SELECT
    @text AS Output,
    DATALENGTH(@text) AS Length;

The query above defines  NVARCHAR data type with 100 bytes of data.

It returns the  string length of 68 because  NVARCHAR takes 2 bytes per character.

• Storing example:

CREATE TABLE UserComments(
    ID int IDENTITY (1,1),
    [Language] VARCHAR(50),
    [Comment] VARCHAR(200),
    [NewComment] NVARCHAR(200));INSERT INTO UserComments ([Language],[Comment],[NewComment]) VALUES ('English','Hello World', N'Hello World');INSERT INTO UserComments ([Language],[Comment],[NewComment]) VALUES ('Japanese','こんにちは世界', N'こんにちは世界');INSERT INTO UserComments ([Language],[Comment],[NewComment]) VALUES ('Hindi','नमस्ते दुनिया', N'नमस्ते दुनिया');SELECT * FROM UserComments;

原文: https://dev.to/ranggakd/what-is-the-n-prefix-in-mssql-all-about-44kf