Oracle Joins: A Comprehensive Comparison of Conventional and ANSI Syntax
Introduction
Oracle's long-standing conventional join syntax, using the ( ) operator, has recently faced competition from the ANSI-compliant syntax. While both approaches produce similar results, there are subtle differences that warrant examination.
Query Performance
Both conventional and ANSI syntax can perform equally well in most scenarios. However, the conventional syntax may suffer limitations in certain situations. For instance, in multi-column outer joins, a misplaced ( ) can lead to an accidental normal join rather than the intended outer join.
Application Compatibility
If your existing codebase is heavily reliant on the conventional syntax, it may not be feasible to migrate to ANSI syntax without incurring interoperability issues. Leaving the code as-is ensures continuous functionality.
Syntax Clarity
ANSI syntax is generally considered cleaner and less prone to errors. It eliminates the need for remembering the ( ) operator in outer joins, reducing the likelihood of incorrect query construction.
Standard Compatibility
ANSI syntax aligns with the SQL standard, facilitating easier code portability across different RDBMS products. If you plan to use other RDBMS platforms in the future, adopting ANSI syntax may prove beneficial.
Migration Considerations
Migrating 200 packages and procedures from conventional to ANSI syntax is a significant undertaking. While there are freeware tools available to automate this process, you should carefully assess the potential impact on application stability.
Recommendations
If your code is functioning properly with conventional syntax, it may not be necessary to convert to ANSI. However, if you prioritize clarity, standard compliance, and ease of interoperability across RDBMS platforms, ANSI syntax should be considered.
Example
| Join Type | Conventional Syntax | ANSI Syntax |
|---|---|---|
| Inner Join | SELECT * FROM emp, dept WHERE emp.deptno = dept.deptno | SELECT * FROM scott.emp INNER JOIN scott.dept ON emp.deptno = dept.deptno |
| Left Outer Join | SELECT * FROM emp, dept WHERE emp.deptno = dept.deptno( ) | SELECT * FROM scott.emp LEFT OUTER JOIN scott.dept ON emp.deptno = dept.deptno |
| Right Outer Join | SELECT * FROM emp, dept WHERE emp.deptno( ) = dept.deptno | SELECT * FROM scott.emp RIGHT OUTER JOIN scott.dept ON emp.deptno = dept.deptno |
| Full Outer Join | SELECT * FROM emp e LEFT OUTER JOIN dept d ON e.deptno( ) = d.deptno UNION ALL SELECT * FROM emp e RIGHT OUTER JOIN dept d ON e.deptno( ) = d.deptno |
SELECT * FROM scott.emp FULL OUTER JOIN scott.dept ON emp.deptno = dept.deptno |
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