EXISTS (SELECT * ) or EXISTS (SELECT 1): Which Subquery Syntax Improves Readability?

Which EXISTS Subquery Syntax Enhances Readability?

When writing subqueries using the EXISTS operator, the question of which syntax is easier to read arises. While performance remains unaffected, the choice between EXISTS (SELECT *) and EXISTS (SELECT 1) warrants consideration.

The documentation of various RDBMS suggests a preference for EXISTS (SELECT *). However, some users find EXISTS (SELECT 1) more intuitive as it explicitly conveys the notion of "if at least one exists."

One argument in favor of EXISTS (SELECT *) is its conciseness. By omitting the specific value 1, it emphasizes the fact that the existence of any value in the subquery is sufficient. This view is supported by the fact that the ANSI standard does not specify the selection within the subquery, leaving it up to the database engine to determine which values to return.

On the other hand, proponents of EXISTS (SELECT 1) argue that it avoids potential confusion. By explicitly stating the value 1, it eliminates any ambiguity as to what the subquery is checking for. It also aligns with common coding practices where the value 1 often represents "true" or "present."

Ultimately, the choice between these two syntaxes is a matter of personal preference. Both are equally valid and provide the same functionality. However, by understanding the underlying semi-join operation and the potential benefits of concise syntax, developers can make an informed decision regarding which approach enhances readability in their specific context.

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