What is the difference between char and varchar?

It is very convenient for CHAR to store fixed-length data, and the indexing efficiency of CHAR fields is high. For example, if char (10) is defined, no matter whether the data you store reaches 10 characters, it takes up to 10 characters.

To store variable-length data, but the storage efficiency is not as high as CHAR. If the possible value of a field is not fixed, we only know that it cannot exceed 10 bytes. defining it as VARCHAR (10) is the most cost-effective. The actual length of the VARCHAR type is the actual length of its value plus (1-2) bytes. Why + (1-2? This 1 ~ Two bytes are used to save the actual length.