Sasha wrote :

Hi,

Let's have a look at this real-life example : I have a login table with one line per login, and some customization preferences (for reportings purposes, which columns are displayed among 12 available slots) :

table LOGIN ( login char(10), password char(10), report char(12) )

If you want a visual idea of the form behind, you can have a live example at http:/onesite.org/observer/customize.php3?login=test7&password=test7

I use the nth character of the column report to know what's displayed in the nth column. I could use an array here.

The alternative solution is to have another table which looks like

REPORT (login_id int, column_id smallint, whats_displayed char(1))

The drawbacks are :

- first there is no advantage in my specific case to use a normalized design - this makes the model a bit more complex - forces me to use an incremental integer column to join the tables, as I could use the login itself as a primary key if it's not referenced elsewhere - I need to insert into/update two tables at the same time, which could lead to integrity problems until mysql can deal with transactions

To sum up, I use a string which is an array of characters, which is fine in my case but some people may need arrays of other datatypes.

A normalized model is better if the number of items in the array is not fixed, but if it's a constant, it's more efficient and easier than another table (and nicer than several columns !)

Regards, Alain