Finding missing tables to avoid cross joins

the user in my application can choose freely some fields from the database.

people
+ peopleid
+ peoplename

cars
+ carid
+ carnumber
+ carcolor

pers_car
+ cari开发者_开发百科d
+ peopleid

Lets assume the user is selecting the fields peoplename and carcolor to find out which person likes which colours.

Is it possible to identify the missing pers_car-Table (needed for joining) if...

• the table and the fields doesn't have a nice name?
• differenciate between logical and unlogical requests from user?

The first word in line (before "+") is the table name. The software removed my line breaks :(