What is meant by Secondary Key?Watch
Is it like a composite key? or is it an index of all primary keys? or something different?
Some help would be appreciated : )
For example, if you had the fields
Employee_ID would likely be the primary key, but the NI number and phone number are highly likely to be unique as well, so you COULD technically set them to primary key. You probably don't want to though as you have the ID field, so that becomes the primary key and the other candidates become secondary keys.
Note that the name would not be considered a secondary key because there isn't really a guarantee that a name would be unique.