1 to 1- A single row of first table associates with single row of second table. for ex- a relationship between person and passport table is one to one because a
person can have only one passport and passport is assign to only one person. 1 to many-A single row of first table associates with more than one rows of second table. for ex- relationship between customer and order table is one to many because customer can place many orders but order can be placed by single customer alone.