Is it any row uniquely identify is superkey

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I have doubt on superkey that is any combination of fields is uniquely identify the

each row or any row in table.

must be each row uniquely identify or any row uniquely identify is superkey

What I have tried:

I have doubt on superkey that is any combination of fields is uniquely identify the 

each row or any row in table.

must be each row uniquely identify or any row uniquely identify is superkey

Posted 1-Sep-17 5:08am

Ramesh p

Updated 1-Sep-17 5:29am

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Wendelius · Answer 1 · 2017-09-01T05:29:00

Solution 1

Superkey is a list of columns that defines a unique combination for the values. There is always one superkey, all columns, but there can also be several other superkeys for a table.

Have a look at Superkey - Wikipedia[^]

Posted 1-Sep-17 5:29am

Wendelius

Comments

Ramesh p 1-Sep-17 11:59am

my doubt is set of columns is uniquely identify any row in the table is super key or each row uniqely identify is super key.

Wendelius 1-Sep-17 14:19pm

If I understand your question correctly, superkey means that this set of column uniquely identifies all rows.

For example

PersonId, unique
FirstName, can contain duplicates
LastName, can contain duplicates

PersonId FirstName LastName
1 John Doe
2 Jane Doe
3 John Other
4 Jane Other
5 Someone Else

Even though FirstName, LastName combination is unique for row 5, superkeys would only be
- PersonId
- PersonId, FirstName
- PersonId, LastName
- PersonId, FirstName, LastName

Ramesh p 2-Sep-17 8:17am

Thank u .i have another doubt on superkey.Forsuppose

Empid Empname
1 Null
2 Ramesh
3 Kumar
4 Null
these {empid,empname} consideras superkey or not.please help me

Wendelius 2-Sep-17 8:37am

EmpId combined with EmpName would be a superkey since EmpId makes it unique even if the Empname is the same