Re: physical bytes

[Rick James]

CHAR(10) always takes 10 or 30 bytes.
VARCHAR(10) takes 1 to 11 or 1 to 31 bytes, depending on size of string.

The first numbers (10,1,11) refer to 1-byte character sets, such as latin1 or ascii.

The later numbers (30,1,31) refer to utf8. A 10-character Chinese phrase would take 30 bytes for the string itself. English: 10; French/Spanish/German: usually not much more than 10, never more than 20.

MyISAM takes another _bit_ for NULL.

InnoDB always adds 1 or 2 bytes per field; I think this includes NULLness. CHAR may act more like VARCHAR. The 1 vs 2 depends on how big the largest field is in the schema.

There is at least one SQL_MODE that impacts what I have said above.

Bottom line (and much simpler): Use CHAR for things that are really fixed length; else use VARCHAR (or TEXT, etc)