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Difference between Equi Join and Outer Join [message #112019] Tue, 22 March 2005 08:07 Go to next message
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Registered: March 2005
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What is the difference between Equi Join and Outer Join?

Re: Difference between Equi Join and Outer Join [message #112117 is a reply to message #112019] Wed, 23 March 2005 02:24 Go to previous message
Messages: 7064
Registered: December 2001
Senior Member
From the Oracle9i SQL Reference:

An equijoin is a join with a join condition containing an equality operator. An equijoin combines rows that have equivalent values for the specified columns. Depending on the internal algorithm the optimizer chooses to execute the join, the total size of the columns in the equijoin condition in a single table may be limited to the size of a data block minus some overhead. The size of a data block is specified by the initialization parameter DB_BLOCK_SIZE.
SELECT last_name, job_id, departments.department_id, department_name
   FROM employees, departments
   WHERE employees.department_id = departments.department_id;

An outer join extends the result of a simple join. An outer join returns all rows that satisfy the join condition and also returns some or all of those rows from one table for which no rows from the other satisfy the join condition.
SELECT d.department_id, e.last_name
   FROM departments d LEFT OUTER JOIN employees e
   ON d.department_id = e.department_id
   ORDER BY d.department_id;

------------- -------------------------
           10 Whalen
           20 Hartstein
           20 Fay
           30 Raphaely
Users familiar with the traditional Oracle outer joins syntax will recognize the same query in this form:
SELECT d.department_id, e.last_name
   FROM departments d, employees e
   WHERE d.department_id = e.department_id(+)
   ORDER BY d.department_id;

At http://tahiti.oracle.com, you can find the Oracle manuals. The site requires a free subscription (it's worth it)


[Updated on: Wed, 23 March 2005 02:25]

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