Calculation of the size of an index created by mysql varchar and char

The size of the mysql varchar and char indexes is calculated when mysql creates an index in varchar, www.2cto.com determines the number of bytes occupied Based on the character set and defined characters. If it is varchar (20) charset = utf8, then key_len is 6320*3 + 1 (whether it is an empty identifier) + 2 (how long the character length is) if it is char (20) charset = gbk then key_len is 4120*2 + 1 (whether it is an empty ID) if it is varchar (20) not null charset = utf8 then key_len will be 6220*3 + 2 (character length) if it is char (20) not null charset = gbk then key_len will be 4020*2 = 40