Consider a relational table with different columns, what would you call the collection of unique and not null values, super key or candidate key?
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Well, what are the definitions of the terms? What did googling your question give? – philipxy Aug 04 '17 at 12:36
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Possible duplicate of [Superkey, candidate key & primary key](https://stackoverflow.com/questions/8337309/superkey-candidate-key-primary-key) – philipxy Aug 04 '17 at 13:01
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Does this answer your question? [Does an empty SQL table have a superkey? Does every SQL table have one?](https://stackoverflow.com/questions/46024902/does-an-empty-sql-table-have-a-superkey-does-every-sql-table-have-one) – philipxy Mar 16 '22 at 00:07
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A Super key is a set or one of more columns to uniquely identify rows in a table.
Candidate keys are selected from the set of super keys, the only thing we take care while selecting candidate key is: It should not have any redundant attribute. That’s the reason they are also termed as minimal super key.
In Employee table there are Three Columns : Emp_Code,Emp_Number,Emp_Name
Super keys:
All of the following sets are able to uniquely identify rows of the employee table.
{Emp_Code}
{Emp_Number}
{Emp_Code, Emp_Number}
{Emp_Code, Emp_Name}
{Emp_Code, Emp_Number, Emp_Name}
{Emp_Number, Emp_Name}
Candidate Keys:
As I stated above, they are the minimal super keys with no redundant attributes.
{Emp_Code}
{Emp_Number}
As a Summary:
A Superkey is a set of columns that uniquely identifies a row.Whereas a Candidate key would be a MINIMAL set of columns that uniquely identifies a row. So essentially a Superkey is a Candidate key with extra unnecessary columns in it.
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A CK is a superkey. So a superkey does not necessarily have more coluns thana a CK. – philipxy Aug 04 '17 at 12:33