SELECT * or SELECT 1 in EXISTS Subqueries: Which is More Readable?

Readability in EXISTS Subqueries: A Comparison

The purpose of this article is to explore the readability differences between using SELECT * and SELECT 1 within EXISTS subqueries. While there is no performance advantage to either syntax, their use can impact the comprehensibility of the query.

SELECT * vs. SELECT 1

The most common syntax used in EXISTS subqueries is SELECT , as evidenced by the popularity of SELECT queries in commercial RDBMS and SO code searches. However, some argue that SELECT 1 is more intuitive, as it explicitly states the intention of checking for the existence of at least one row.

Intuitive Interpretation

The SELECT * syntax implies that the contents of the subquery are irrelevant. The sole focus is on the existence of a row in the subquery table. In contrast, SELECT 1 directly checks for the truthfulness of the condition, making it more explicit and potentially easier to understand.

ANSI Standard

The ANSI SQL standard states that the choice between SELECT * and SELECT 1 within EXISTS subqueries is irrelevant. This reinforces the fact that the performance and functionality of the query remain the same regardless of the syntax used.

Alternative Perspective

Beyond readability, it is important to recognize that EXISTS is a semi-join operation. Instead of returning the actual rows from the subquery, it simply indicates whether any rows exist that satisfy the join condition. This understanding deepens one's comprehension of the query's behavior.

The above is the detailed content of SELECT * or SELECT 1 in EXISTS Subqueries: Which is More Readable?. For more information, please follow other related articles on the PHP Chinese website!