External key to MySQL
The outer key in MySQL, in the idea, adds a line from one table to another if the second one matches the external key?
Alberto last edited by
Well, that's the way the questions are formulated to make them understand yourself. "When the fire burns, it's in the bay," it's called readers, each in its own way. All I've learned is that the question sounds outside. I answer as I can.
The outer key is a reference to the parent: each of the occupants of the house points to the house where he lives; and the house not only knows nothing about his tenants, it doesn't even suspect that they exist. The external key is a duplicate of the primary key, a unique set of values of the fields (fields) of the parent table. Maintains data integrity and relationship between nature (tables)