When you join two tables using a relationship, you establish criteria that FileMaker Pro Advanced uses to display or access related records.
Your criteria can be simple, such as matching a field in TableA with a field in TableB with equal values. A more complex relationship definition usually returns a narrower set of related records. Examples of complex relationships include using multiple match fields on one or both sides of the relationship, comparing match fields using non-equal relational operators, or using calculated match fields.
The following table describes the types of criteria you can use when creating relationships.
Relationship type  | Description  | 
Single-criteria  | Relates two tables based on a single common value, such as a serial number or an ID number. See Single-criteria relationships.  | 
Multicriteria  | Relates two tables based on more than one common value, such as a customer ID and a date. See Multicriteria relationships.  | 
Comparative criteria  | Uses one or more relational operators to compare match field values in two related tables. See Relationships that use comparative operators.  | 
Range of records  | Similar to a multicriteria relationship, it uses comparative operators to find a range of records that are greater than one criteria and less than the other criteria. See Relationships that return a range of records.  |