thanks for the reply
binoj daniel, January 22, 2018 - 11:52 pm UTC
Thanks for the replay Connor,
but still... if not referred with a foreign key , Primarykey-EmpId and Unique key-Mobilenumber could be changeable.
So how can we say primary key is immutable ?
*implementation* could be defined more clear?
Thanks
Binoj Daniel
January 23, 2018 - 2:00 am UTC
By "implementation" I mean that to provide the *functionality*, ie, stop people from entering a duplicate, we will implement the primary key and unique key in a similar way, ie, with an underlying index.
But the concept is different - one identifies the row, the other ensures that the a column cannot contain duplicates.