Does Switching to ANSI JOIN Syntax Improve SQL Query Performance?

ANSI JOIN Syntax in SQL: A Performance Analysis

SQL utilizes JOIN syntax to link tables via matching columns. Two primary approaches exist: the established non-ANSI style and the more modern ANSI JOIN style. This article explores whether substituting non-ANSI joins with their ANSI equivalents results in performance enhancements.

The example query uses both non-ANSI and ANSI JOIN methods to connect tables. The underlying query logic remains consistent; however, the ANSI version separates join conditions (JOIN clauses) from filtering conditions (WHERE clause), improving readability.

Performance Evaluation

Despite the different syntaxes, both query types should produce identical internal query plans. The benefits of ANSI JOIN syntax are primarily:

• Enhanced Readability: Isolating join conditions simplifies query comprehension.
• Ambiguity Elimination: ANSI syntax clarifies potential ambiguities inherent in non-ANSI outer join syntax.
• Standard Adherence: ANSI syntax is the preferred standard among developers and database administrators, promoting consistency.
• Improved Safety: ANSI JOIN syntax reduces the risk of unintentional cross joins.

Recommended Best Practice

While the older non-ANSI syntax might seem intuitively familiar to some, the advantages of ANSI JOIN syntax in terms of clarity, ambiguity avoidance, and industry-standard compliance make it the recommended approach.

Exception: Natural Joins

The only situation where deviating from ANSI JOIN syntax might be considered is when using natural joins, which can introduce potential complexities and risks.

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