Should You Use ORDER BY in Subqueries?

Pitfalls of Employing ORDER BY in Subqueries

Despite its intuitive appeal, utilizing the ORDER BY clause within a subquery is generally discouraged due to several conceptual inconsistencies.

Why it Doesn't Make Sense

The purpose of a subquery is to return a set of data that is then incorporated into a larger outer query. To ensure consistency, the order of results obtained from the subquery remains irrelevant, as the outer query will ultimately define the final ordering.

Implementation-Specific Quirks

Although some database management systems (DBMSs) may exhibit peculiar behavior in response to ORDER BY in subqueries, relying on such implementation-specific quirks is ill-advised. Database results are inherently unordered unless explicitly specified through an ORDER BY clause in the outer query. Therefore, even if the subquery employs ORDER BY, it offers no guarantee of influencing the order of the final results.

Exception for LIMIT and TOP

Note that if the subquery includes a LIMIT or TOP clause, an ORDER BY might become necessary. However, these constructs are not part of standard SQL and are therefore not universally supported.

Conclusion

While it may be tempting to use ORDER BY in a subquery, it is ultimately a redundant and potentially confusing practice. The ordering of results should be handled by the outer query, ensuring consistency and preventing unnecessary complexity in subqueries.

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