MySQL的char与varchar_MySQL

CREATE TABLE `varcharLessThan4` (`lastName` varchar(3)) ;mysql> desc varcharLessThan4;+----------+---------+------+-----+---------+-------+| Field| Type| Null | Key | Default | Extra |+----------+---------+------+-----+---------+-------+| lastName | char(3) | YES| | NULL| |+----------+---------+------+-----+---------+-------+1 row in set (0.01 sec)CREATE TABLE `charGreaterThan4` (`firstName` char(4),`lastName` varchar(4)) ;mysql> desc charGreaterThan4;+-----------+------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-----------+------------+------+-----+---------+-------+| firstName | varchar(4) | YES| | NULL| || lastName| varchar(4) | YES| | NULL| |+-----------+------------+------+-----+---------+-------+2 rows in set (0.00 sec)CREATE TABLE `charLessThan4` (`firstName` char(3),`lastName` varchar(4)) ;mysql> desc charLessThan4;+-----------+------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-----------+------------+------+-----+---------+-------+| firstName | char(3)| YES| | NULL| || lastName| varchar(4) | YES| | NULL| |+-----------+------------+------+-----+---------+-------+2 rows in set (0.00 sec)

Note that using CHAR will only speed up your access if the whole record is fixed size. That is, if you use any variable size object, you might as well make all of them variable size. You gain no speed by using a CHAR in a table that also contains a VARCHAR.