Re: [PHP] Mysql/php database performance question

[Marek Kilimajer]

seems to be a little bit more complicated:

CREATE TABLE `aa` (
`id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`aaa` CHAR( 50 ) NOT NULL ,
`bbb` CHAR( 50 ) NOT NULL
);

both aaa and bbb are char now


CREATE TABLE `aaa` (
`id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`aaa` CHAR( 50 ) NOT NULL ,
`bbb` VARCHAR( 255 ) NOT NULL
);

aaa will be varchar anyway

CREATE TABLE `aaa` (
`id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`aaa` CHAR( 50 ) NOT NULL , );

aaa is char

ALTER TABLE `aaa` ADD `bbb` VARCHAR( 250 ) NOT NULL ;

aaa in now VARCHAR

Seems like one cannot mix char and varchar columns in one table

Matt Schroebel wrote:

-----Original Message-----
From: Marek Kilimajer [mailto:[EMAIL PROTECTED]] Sent: Friday, January 10, 2003 11:45 AM
To: Matt Schroebel
Cc: Simon Dedeyne; [EMAIL PROTECTED]
Subject: Re: [PHP] Mysql/php database performance question


Sure, just tried it (32-bit platform, might be >7 for 64-bits).
I have a feeling it is somewhere in the manual.

How'd you try it?
I created a 1 column 42 char record in phpMyAdmin. Everytime I add a
row, regardless of size the dataspace increases by 42.

With a second table, with 1 column varchar(42), each 4-5 char insert
resulted in 20 bytes of space (must be some minimum overhead), and a
full 42 resulted in 44 bytes of dataspace used.

I'm curious here, as it seems the trade off is speed of access with char
[and the overhead of removing trailing spaces on each retrieval] vs
storage size in varchar [and it's improved strip right spaces on storage
only happening once]. That's what the man page I pointed to last time
said. There are some examples of truncating data to 4 bytes on that
page but no mention of storing char as varchar.

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