Natural join

From Oracle FAQ

A natural join is a join statement that compares the common columns of both tables with each other. One should check whether common columns exist in both tables before doing a natural join.

Natural joins may cause problems if columns are added or renamed. Also, no more than two tables can be joined using this method. So, it is best to avoid natural joins as far as possible.

[edit] Examples

This is the same as an equi join on (emp.deptno = dept.deptno):

SELECT dname, ename FROM dept NATURAL JOIN emp

Same query on the HR sample schema:

SELECT department_name, first_name||' '||last_name
  FROM departments NATURAL JOIN employees;

[edit] Also see

• Cartesian join
• Equi join
• Inner join
• Nonequi join
• Outer join
• Self join

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