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;
DEPARTMENT_ID LAST_NAME
------------- -------------------------
10 Whalen
20 Hartstein
20 Fay
30 Raphaely
...
250
260
270Users 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)
MHE
[Updated on: Wed, 23 March 2005 02:25]
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