The difference between char varchar and nvarchar in SQL

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Char
char is fixed-length, that is , when you enter a character that is less than the number you specify, char (8), the character you enter is less than 8 o'clock, and it will then fill the empty value back. When you enter a character that is larger than the specified number, it intercepts the characters that are out of the bounds.
nvarchar (n)
A variable-length Unicode character data that contains n characters. the value of n must be between 1 and 4,000. The storage size of bytes is twice times the number of characters entered. The input data character length can be zero.
varchar[(N)]
variable-length, non-Unicode character data with a length of n bytes. n must be a numeric value between 1 and 8,000. Storage size is the actual length of bytes of input data, not n bytes. The input data character length can be zero.
1, CHAR. Char is convenient for storing fixed-length data, and the index on a char field is highly efficient, such as defining char (10), which takes up 10 bytes of space regardless of whether the data you store is 10 bytes.

2, VARCHAR. Store variable-length data, but the storage efficiency is no higher than char. If the possible value of a field is not fixed length, we only know that it cannot exceed 10 characters, it is the most advantageous to define it as VARCHAR (10). The actual length of the varchar type is +1 of the actual length of its value. Why "+1"? This byte is used to hold the length that is actually used.
From the space consideration, with the varchar suitable, from the efficiency consideration, uses the char to be suitable, the key is to find the tradeoff point according to the actual situation.
3, TEXT. Text stores non-Unicode data of variable length, with a maximum length of 2^31-1 (2,147,483,647) characters.
4, NCHAR, NVARCHAR, NTEXT. These three kinds of names from the first three more than the previous "N". It represents a character stored in a Unicode data type. We know that characters, the English character only need a byte storage is enough, but the number of Chinese characters, need two bytes of storage, English and Chinese characters at the same time prone to confusion, the Unicode character set is to solve the character set this incompatibility problem, all of its characters are expressed in two bytes, That is, the English character is also represented in two bytes. The length of the nchar and nvarchar is between 1 and 4000. Compared to char and varchar, nchar and nvarchar store up to 4,000 characters, whether in English or Chinese characters, while char and varchar can store up to 8,000 English and 4,000 Chinese characters. It can be seen that the use of nchar, nvarchar data types without worrying about the input characters are English or Chinese characters, more convenient, but in the storage of English number of some losses.
So generally, if it contains Chinese characters, use Nchar/nvarchar, if pure English and numbers, with Char/varchar.

The difference between char varchar and nvarchar in SQL