Oracle Joins: Conventional ( ) vs. ANSI Syntax – Which Should You Choose?

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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