On Wed, Jan 7, 2009 at 9:17 AM, David Giragosian <dgiragos...@gmail.com> wrote: > On 1/7/09, Jim Lyons <jlyons4...@gmail.com> wrote: >> >> There are other factors. If a table is completely fixed in size it makes >> for a faster lookup time since the offset is easier to compute. This is >> true, at least, for myisam tables. All books on tuning that I have read >> have said the CHAR makes for more efficient lookup and comparison that >> VARCHAR. >> >> Also, I was told by the instructor at a MySQL class that all VARCHAR >> columns >> are converted to CHAR when stored in memory. Can anyone else confirm this? > > > That's my recollection, also, derived from a MySQL class. IIRC, the char > length is equal to the longest varchar record in the column.
Actually it's a fixed-length buffer big enough to hold the worst-case possible value, not the worst-case existing value. In bytes, no less. If it's a utf8 varchar(100), that's 300 bytes, even if the biggest value in the table is one character. -- Baron Schwartz, Director of Consulting, Percona Inc. Our Blog: http://www.mysqlperformanceblog.com/ Our Services: http://www.percona.com/services.html -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
