Differences and relations between varchar and nvarchar in database

        When creating a new table in the database, some field types are found with n Some don't n, So what's the difference between the two ？
         So I went online to find some information as follows ：
One 、
1、CHAR.CHAR It's very convenient to store fixed length data ,CHAR The index on the field is of high efficiency , Like defining char(10), So whether or not the data you store reaches 10 Bytes , Take it all 10 Bytes of space , The insufficient space is filled in automatically , So it may be used many times when reading trim（）.

2、VARCHAR. Store variable length data , But storage efficiency is not CHAR high . If the possible value of a field is not of fixed length , All we know is that it can't exceed 10 Characters , Define it as VARCHAR(10) Is the most cost-effective .VARCHAR The actual length of a type is the actual length of its value +1. Why? “+1” Well ？ This byte is used to store the actual length used . From the perspective of space , use varchar appropriate ; Considering efficiency , use char appropriate , The key is to find the trade-off point according to the actual situation .

3、TEXT.text Store variable length non Unicode data , Maximum length is 2^31-1(2,147,483,647) Characters .

4、NCHAR、NVARCHAR、NTEXT. These three are more than the first three in terms of names “N”. It means that the storage is Unicode The character of the data type . We know that in characters , English characters need only one byte to store , But there are many Chinese characters , It takes two bytes to store , It is easy to cause confusion when English and Chinese characters exist at the same time ,Unicode Character set is to solve the problem of character set incompatibility , All of its characters are represented in two bytes , In other words, English characters are also represented by two bytes .nchar、nvarchar The length of is 1 To 4000 Between . and char、varchar Compare ,nchar、nvarchar At most 4000 Characters , Whether in English or Chinese ; and char、varchar It can store at most 8000 English ,4000 The Chinese characters . It can be seen that the nchar、nvarchar Don't worry about whether the input character is English or Chinese , More convenient , But there is some loss in the amount of English stored .

So generally speaking , If it contains Chinese characters , use nchar/nvarchar, If it's pure English and numbers , use char/varchar

Their differences can be summarized as ：

CHAR,NCHAR Fixed length , Fast , Take up a lot of space , Need to be dealt with

VARCHAR,NVARCHAR,TEXT Indefinite length , Small space , Slow speed , No need to deal with

NCHAR、NVARCHAR、NTEXT Handle Unicode code

Reference article ：​ ​ Click to open the link ​​

Two 、

        varchar stay SQL Server In, a single word section is used to store data ,nvarchar It's using Unico To store data ． Chinese characters are stored in SQL Server Will be saved as two bytes （ It is generally used Unico code ）, English characters are saved in the database , If the field type is varchar, Then only one byte will be occupied , If the field type is nvarchar, Will occupy two bytes ． 

         Under normal circumstances , We use varchar Chinese characters can also be stored , However, if the operating system is English and the support for Chinese Fonts is not comprehensive , stay SQL Server Store Chinese characters as varchar There will be chaos ( Is shown as ??)． And under normal circumstances , The host will support Chinese environment , So if you use varchar To store data , It cannot be found in the development stage ． Most of the time , There will be no problem when deploying ．

         But if the host deployed is an English operating system , And does not support Chinese environment , Then the problem arises ． be-all varchar Fields will become garbled when storing Chinese （ Is shown as ??）． And generally, you won't know that this is because you use the wrong data type to store , You will try to install Chinese fonts , Try to set the language environment of the operating system ．．． None of these can solve the problem , The only way to solve the problem is to personalize the type of database fields as nvarchar（ perhaps nchar）． Friends who are familiar with project management should know , It is a terrible thing to modify the database at the deployment stage ．

　　 Use nvarchar Another great advantage of is that you don't need to consider the differences between Chinese and English characters when judging strings ．

　　 Of course , Use nvarchar Storing English characters will double the storage space ． But when the cost of storage is already very low , Giving priority to compatibility will bring you more benefits ．

　　 So in Design You should try to use nvarchar To store data ． Only when you make sure that this field will not save Chinese , Just use varchar To store ． 

        Generally speaking , If it contains Chinese characters , use nchar/nvarchar, If it's pure English and numbers , use char/varchar

Reference article ：​ ​ Click to open the link ​​

        Unicode Character set is to solve the problem of character set incompatibility , All of its characters are represented in two bytes , In other words, English characters are also represented by two bytes .