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 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
>
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Jim Lyons
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