How Does the Oracle ' ' Operator Work in SQL Joins?

Oracle's " " Operator: A Guide to Outer Joins in SQL

Oracle SQL employs the " " operator to execute outer joins, merging data from multiple tables based on a defined join condition. This operator provides a concise way to combine data, but newer standards offer improved clarity and readability.

The " " operator, placed at the end of a join condition, designates a right outer join. This means all rows from the right table are included in the result, even without matching rows in the left table. The left table acts as the primary table, and the right table as the secondary.

Illustrative Example:

Consider this SQL statement:

<code class="language-sql">select ...
from a, b
where a.id = b.id(+)</code>

This performs a right outer join between tables "a" and "b" using the "id" column. The query returns all rows from table "b", and any matching rows from table "a". If a row in "b" lacks a match in "a", its corresponding columns will show NULL values.

Comparison with ANSI JOIN Syntax:

Oracle's " " operator offers an alternative to the more standard ANSI-92 syntax for outer joins. ANSI-92 uses "LEFT JOIN" and "RIGHT JOIN" keywords for greater clarity. The ANSI-92 equivalent of the example above is:

<code class="language-sql">SELECT ...
FROM b
RIGHT JOIN a ON a.id = b.id</code>

Best Practices:

While the " " operator functions correctly, Oracle recommends using the ANSI-92 syntax ("LEFT JOIN", "RIGHT JOIN", etc.). This syntax is more widely accepted, enhances code readability, and aligns with industry best practices. Adopting the ANSI-92 standard improves code maintainability and collaboration.

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