MySQL VARCHAR Lengths and UTF-8
In MySQL, if I create a new VARCHAR(32) field in a UTF-8 table does it means I can store 32 bytes of data in that field or 32 chars (multi-byte)?
This answer showed up at the top of my google search results but wasn't correct so:
The confusion is probably due to different versions of mysql being tested.
- Version 4 counts bytes
- Version 5 counts characters
http://dev.mysql.com/doc/refman/5.0/en/string-type-overview.html
MySQL interprets length specifications in character column definitions in character units. (Before MySQL 4.1, column lengths were interpreted in bytes.) This applies to CHAR, VARCHAR, and the TEXT types.
Interestingly (I hadn't thought about it) the max length of a varchar column is affected by utf8 as follows:
The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used. For example, utf8 characters can require up to three bytes per character, so a VARCHAR column that uses the utf8 character set can be declared to be a maximum of 21,844 characters.
it would let you store 32 multi-byte chars
To save space with UTF-8, use VARCHAR instead of CHAR. Otherwise, MySQL must reserve three bytes for each character in a CHAR CHARACTER SET utf8 column because that is the maximum possible length. For example, MySQL must reserve 30 bytes for a CHAR(10) CHARACTER SET utf8 column.
http://dev.mysql.com/doc/refman/5.0/en/charset-unicode.html
32 multibytes data for varchar(32) with collation utf8_unicode_ci, I just tested with XAMPP.
１２３４５６７８９０１２３４５６７８９０１２３４５６７８９０１２３４５６７８９０
Get truncated to:
１２３４５６７８９０１２３４５６７８９０１２３４５６７８９０１２
Keep in mind that these are not regular ASCII chars.
It is better to use "char" for high-frequent update tables because the total data length of the row will be fixed and fast. Varchar columns make row data sizes dynamic. That's not good for MyISAM, but I don't know about InnoDB and others. For example, if you have a very narrow "type" column, it may be better to use char(2) with latin1 charset to only claim minimal space.