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? On Wed, Jan 7, 2009 at 7:26 AM, Richard Heyes <rich...@php.net> wrote: > >>So where's the advantage of VARCHAR ? > > > > Less space on disc = less data retrieved from disc = faster data > > retrieval - sometimes. If you have small columns, a small number of > > rows, or both, then char columns may be faster. If you have large > > columns of varying actual length, lots of rows, or both, then varchar > > columns may be faster. > > I still think a CHAR field would be faster than a VARCHAR because of > the fixed row length (assuming every thing else is fixed). Perhaps > someone from the MySQL list could clarify...? > > -- > Richard Heyes > > HTML5 Graphing for FF, Chrome, Opera and Safari: > http://www.rgraph.org (Updated January 4th) > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/mysql?unsub=jlyons4...@gmail.com > > -- Jim Lyons Web developer / Database administrator http://www.weblyons.com
