Running Dynamic Queries

I'm creating a search function right now and I'm running into a problem where my search function doesn't know what fields the user will search for, and therefore doesn't know whether or not to put quote marks around specific values or not.

For example, somebody might search for somebody else with year of birth in which case I might have a query:

SELECT userid FROM users WHERE yob = 1970

but somebody else might search for a name, in which case I need

SELECT userid FROM users WHERE first_name = 'Andrew'

or somebody else might search for both and need

SELECT userid FROM users WHERE yob = 1970 AND first_name = 'Andrew'

I'm accomplishing this by having the function (this is in PHP) take an array as an argument, where the key is the MySQL column and the value is the required value for that column. So in the 3rd example, it would be a 2-item array:

yob => 1970
first_name => 'Andrew'

And then cycling through that and dynamically creating a MySQL query based on the received array.

So... my problem is finding a way to specify when quote marks are required and when they're not. Is there any way to just have MySQL default to the format of the column? Also, if anybody thinks this isn't the right way to create a search function, let me know because I'm new at this .

Thanks!

PS: Right now what I'm doing is I'm creating arrays that include names of columns that do and don't need quote marks. Then in construcing the MySQL statement I'm checking to see which array a column is in, and making the quote decision based on that.