CODEWITHSUNDEEP
sqlkeyrdbms
Shashank Raghunath
Shashank Raghunath

Reputation: 149

Difference between Primary key and Candidate key

I have read about Keys in RDBMS. https://stackoverflow.com/a/6951124/1647112 I however couldn't understand the need to use a candidate key. If a primary key is all that is needed to uniquely identify a row in a table, why is candidate key required? Please give a good example as to state the differences and importance of various keys. Thanks in advance.

Upvotes: 3

Views: 2736

Answers (2)

Shashank Raghunath
Shashank Raghunath

Reputation: 149

From, the above answer i came to this conclusion

Super key(one or more attributes used for selecting one or more rows)

                        ||
                        \/

Candidate key(one or more attributes from super used for selecting a single row)

                        ||  
                        \/

Primary key(one attribute among candidate keys used for selecting a single row)

Am i correct?

Upvotes: 0

Oded
Oded

Reputation: 499362

A table can have one or more candidate keys - these are keys that uniquely identify a row in the table.

However, only one of these candidate keys can be chosen to be the primary key.

Upvotes: 5

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