Is There a Reliable Default Sort Order in SQL, and What's the Best Practice?

Best Practices for SQL Default Sort Order

In SQL code, it is often assumed that the default sort order is consistent. However, this assumption may lead to unexpected results. This article explores the importance of understanding the default sort order behavior and provides best practices to ensure predictable data retrieval.

FIFO sorting without index

By default, if no index is defined and no ORDER BY clause is specified, a database management system (DBMS) usually uses FIFO (first in, first out) to sort data. This means that the order in which data is inserted into the table will determine the order in which data is retrieved.

Sort order is not always guaranteed

However, it is important to note that FIFO order is not always guaranteed to be preserved. The DBMS may reorder data internally for various reasons, such as performance optimization or table reorganization. Therefore, relying on a specific default sort order may lead to inconsistent results.

Best Practice: Always include an ORDER BY clause

To ensure predictable data retrieval, a best practice is to always include an ORDER BY clause when querying a table. This specifies the desired sort order and ensures that data is returned in a consistent manner.

Summary

While the default sort order can provide initial sorting, it should not be relied upon for predictable data retrieval. By understanding the behavior of the default sort order and implementing the best practice of always including an ORDER BY clause, database developers can avoid unexpected results and ensure that data is presented in the desired order.

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