Why Does MySQL's `GROUP BY` Differ from Standard SQL?

MySQL’s unorthodox “GROUP BY” query method

Unlike Oracle and SQL Server, MySQL allows using "group by" queries without aggregate functions. This behavior violates the ANSI-SQL standard and has long been a source of confusion.

Reasons for MySQL

According to the MySQL Online Manual (version 5.0), this non-traditional approach is implemented for two main reasons:

1. Performance: In many cases, queries without aggregate functions can be executed more efficiently without having to perform additional aggregations.
2. User Convenience: When a query contains non-aggregated columns (such as identifiers or lookup values), it is very convenient to be able to include these columns in the final result without unnecessary aggregation.

Criticisms and Solutions

MySQL's approach has been criticized for not complying with the ANSI-SQL standard. To address these issues, MySQL provides a configuration parameter only_full_group_by that can be set to enforce standard behavior.

Summary

While MySQL’s unconventional approach to “group by” queries has its drawbacks, it also offers advantages in terms of performance and convenience. Developers should be aware of this behavior and use it with caution to ensure accurate and meaningful results.

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