Deep in SQL Server, the difference between fixed length char (n) and variable length varchar (n) is detailed _mssql

char (n) is a fixed-length format in which a field formatted with char (n) occupies an n-character width, and if the actual stored data is longer than N, it will be truncated, if the length is less than n, filled with a blank character.

VARCHAR (n) is a variable-length format in which the field allocates space based on the actual data length and does not waste space, but the speed of searching for data can be a bit cumbersome.

Generally, as long as a table has a field defined as a varchar (n) type, the rest of the fields defined with char (n) are actually varchar (n) types.

If your length itself is not long, such as 3~10 characters, then use char (n) format more efficient, faster search. But if some of the data is very long, some of the data is relatively short, such as the registration of user profiles such fields, there is no way, and very concerned about the waste of space, then use varchar (n) format.