CODEWITHSUNDEEP
databaserelational-databasenatural-join
Amit-dat
Amit-dat

Reputation: 149

What is the new primary key when we apply natural join on two tables?

If there are two tables:

table1 with attributes a1, a2, a3 and table2 with attributes b1, b2, b3. And a1 and b1 being their respective primary keys. What's the new primary key when the natural join is applied on the two tables. Do a1, b1 combine to form a composite primary key or they become two separate candidate keys

Upvotes: 0

Views: 1161

Answers (1)

nvogel
nvogel

Reputation: 25534

In relational database terms the result should have keys corresponding to every key from one relation paired with every key from the other (i.e. the "natural-join" of the candidate keys, not just one key per relation). So if A1 and B1 are the only keys in your example then the only key in the natural-joined result would be (A1,B1).

However, you tagged your question with MySQL. MySQL is a SQL DBMS, not relational. MySQL doesn't support the relational model concept of key derivation. In MySQL there is no physical implementation of any key in the result of such a query.

Upvotes: 6

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