If I wanted to define a table to have a cloumn which is either yes or no for example. Would it be better to use a single char (0 or 1), or can I use an enum (I find them more friendly ;)).
Since enums are internaly stored as numbers, and are therefore fast, it's better to use them than characters. Unless ther's a specific need.
It, for instance, depends on how you're gonna use them in case you select them. For example, if you have enum('yes','no'), and you select it in perl, using them in if statements like this:
if ($sqlref->[0][0]) {
do something;
}
wont work, since, when selected in string context, you're gonna get 'yes', which is true (it will work if one selects it in integer context). But using characters '0' and '1' will always work, string '0' is false in perl.