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This chapter discusses how the Oracle optimizer executes SQL statements that contain joins, anti-joins, and semi-joins. It also describes how the optimizer can use bitmap indexes to execute star queries, which join a fact table to multiple dimension tables.
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Oracle Client/Server Architecture Distributed Processing...
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26 Ιουλ 2013 · An outer join means that Oracle has to make rows on every row. "JOIN" without any term means "INNER JOIN". An OUTER JOIN is only to be used if you need it, as in you want a blank value if there is no matching data.
This tutorial shows you how to use the Oracle LEFT JOIN clause to query data from multiple tables with many practical examples.
LEFT OUTER JOIN example. The following example shows how a partitioned outer join fills data gaps in rows to facilitate analytic function specification and reliable report formatting. The example first creates a small data table to be used in the join. SELECT d.department_id, e.last_name . FROM hr.departments d LEFT OUTER JOIN hr.employees e .
The optimizer processes the join from left to right. For example, if this graphic depicted a nested loops join, then table1 is the outer loop, and table2 is the inner loop.
To write a query that performs an outer join of tables A and B and returns all rows from A (a left outer join), use the ANSI LEFT [OUTER] JOIN syntax, or apply the outer join operator (+) to all columns of B in the join condition.
Outer Joins. An outer join returns all the rows from one table along with the matching rows from the other. Rows without a matching entry in the outer table return null for the outer table's columns. An outer join can either be left or right. The direction defines which side of the join the database preserves the rows for.
