>If I use an incrementing number as a surrogate primary key, why should I make it a character field? Tastrade does that, and I've heard that it's the thing to do. But a key like this is not useful for ordering the records, and therefore would not be part of compound index expressions. Wouldn't it be better to use a double field?

i'd recommend integer. if tastrade has compound keys, they'd use character PKs because the m$ RI code has problems w/ compound keys.