What's the Oracle ( ) Operator and Why Should I Use OUTER JOIN Instead?

Oracle's ( ) Operator: A Legacy Approach to Outer Joins

Consider this SQL statement:

select ...
from a, b
where a.id = b.id(+)

The ( ) operator in Oracle SQL is an older, non-standard way to perform an outer join. It's a holdover from pre-ANSI-92 SQL and is generally considered less readable and potentially less efficient than the modern OUTER JOIN syntax.

Modernizing with ANSI-92 Standard Outer Joins

The above query can be rewritten using the standard and preferred ANSI-92 LEFT JOIN syntax:

SELECT ...
FROM a
LEFT JOIN b ON b.id = a.id

This version is clearer, easier to understand, and more portable across different database systems.

Key Differences and Considerations

The ( ) operator differs significantly from the OUTER JOIN approach:

• Non-Standard: The ( ) operator is not part of the ANSI SQL standard. Using standard syntax improves code readability and maintainability.
• Potential Performance Implications: While both achieve the same result, the ( ) operator might require specific indexing strategies for optimal performance. OUTER JOIN syntax, especially when used with modern query optimizers, often leads to more efficient execution plans.

Oracle's Strong Recommendation: Embrace Standard OUTER JOINs

Oracle explicitly recommends using the standard OUTER JOIN syntax (LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN) instead of the ( ) operator. This is because:

• Improved Performance: Modern database optimizers are better at handling the standard OUTER JOIN syntax, leading to better query performance.
• Standard Compliance: Using standard syntax ensures better portability and reduces the risk of confusion across different database systems and development teams.
• Reduced Errors: The standard syntax is generally less error-prone and easier to understand, leading to fewer coding mistakes.

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