To quote or not to quote?

I guess this is mostly a MySQL question, but perhaps PHP has a solution... I would like a foolproof way to determine whether a data value needs to be quoted. Numeric data doesn't need quotes, but string data does. I could use mysql_field_type and check if it's integer, float, double, real, etc., but this seems fragile. I could easily miss one, or a new version of MySQL could add a new one. So how can I get the equivalent of a "mysql_needs_quotes" function? -- Patrick Doyle doylep@eecg.utoronto.ca