Hi,
There is difference between varchar(63) and varchar(38). Instead of
selecting MAX(LENGTH()) you can do PROCEDURE ANALYZE() on the table,
which will tell you about the optimal record type for the data you
currently have in the table.
When you are using inreasonably large varchar columns, and mysql decides
to create an in-memory temporary table with the MEMORY storage engine,
practically all varchar(n) fields will be converted to char(n) fields,
because memory storage engine doesn't support variable length data.
Peter Boros
On 04/06/2011 08:28 PM, John G. Heim wrote:
Does it make any difference if I allocate a particular number of bytes
for a varchar? I mean, just as an example, maybe its more efficient to
use a power of 2 as the field length. Or maybe power of 2 minus 1. I'm
guessing not and that anything less than 255 is the same.
I'm converting some data in a spreadsheet and I have to create a table
with about 150 columns. So I created all the columns varchar(255) and
now I'm asking mysql to show me the longest value in each column.
"SELECT MAX(LENGTH(column99)) FROM TABLE99". Then I've been modifying
the "CREATE TABLE" code to accomodate the longest value plus a little
more. So if the longest value in the column is 38 characters, I'd
probably make that a VARCHAR(50). But maybe I might as well make that 63
or 64. Or maybe I'm wasting my time and should leave them all 255.
--
MySQL General Mailing List
For list archives: http://lists.mysql.com/mysql
To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
