ANSI vs. Non-ANSI JOINs in SQL: Do Performance Differences Exist?

Analysis of performance differences between ANSI and non-ANSI JOIN statements

SQL provides two different JOIN syntaxes: traditional non-ANSI syntax and newer ANSI-92 compliant syntax. This article explores the difference in query performance between these two syntaxes.

The difference between ANSI and non-ANSI JOIN

Non-ANSI JOIN syntax uses commas to separate tables, while ANSI-92 syntax uses the JOIN keyword and ON clause to specify relationships between tables. However, the underlying join logic of both syntaxes is the same.

Performance comparison

The performance difference between ANSI and non-ANSI JOIN queries is usually negligible. Both typically generate the same query plan, ensuring efficient execution of join operations. However, ANSI-92 syntax has some subtle advantages.

Advantages of ANSI JOIN syntax

• Readability enhancement: ANSI JOIN syntax separates connection logic from filtering logic, making the query structure easier to understand.
• Reduced ambiguity: Non-ANSI syntax may be ambiguous in certain external join cases, leading to unpredictable results. ANSI JOIN syntax eliminates this problem.
• Improved Compatibility: ANSI-92 syntax is the industry standard and all modern query tools support it.
• Avoid accidental cross-connections: ANSI JOIN syntax clearly specifies the connection relationship, reducing the risk of accidental cross-connections.

Suggestion

Based on the above advantages, it is generally recommended to use ANSI-92 JOIN syntax instead of non-ANSI syntax. While the performance difference is negligible, the enhanced readability and reduced likelihood of errors make ANSI JOIN the first choice for most SQL developers.

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