how to represent symmetric many to many relationship

Question

suppose i have a entity called USER and a relationship FRIENDSHIP exist between two USERs SO for that i have a table \'USER\' and a relationship table \'FRIENDSHIP\'

Answer 1

If you store the two rows, you will be required to enforce an integrity rule that ensures that friendships always come in pairs.

Store only one row in the table (say, FR), and create a view SYMFR as

SELECT x,y FROM FR UNION SELECT x as y, y as x FROM FR