A very good artical On candidatekey & Surrogate Key in Sql Databse.
Candidate key is an attribute or a combination of attributes that uniquely identifies each row in the table .
Surrogate Key is an artificially generated unique identifier, which has no relation to the table data .
A key with no business meaning .
Refer :
http://www.sqlservercentral.com/articles/Primary+key/70747/
http://www.agiledata.org/essays/keys.html
