In-depth explanation of differences between fixed-length char (n) and variable-length varchar (n) in SQL Server

Char (n) is a fixed-length format. The field in the format of char (n) occupies a fixed width of n characters. If the actual length of the stored data exceeds n, the excess data is truncated, if the length is less than n, it will be filled with null characters.

Varchar (n) is a variable-length format. Fields in this format allocate space based on the actual data length, without wasting space. However, it is troublesome to search data quickly.

Generally, as long as a table has a field defined as varchar (n), the other fields defined using char (n) are actually varchar (n.

If your length is not long, for example, 3 ~ 10 characters, so the char (n) format is more efficient and the search speed is faster. However, if some data is very long and some data is relatively short, such as the profile of the registered user, there is no way to do it, and you are very concerned about the waste of space, then the varchar (n) format is used.