JOIN vs. INNER JOIN in SQL: Are They Truly Interchangeable?

Explanation of the subtle differences between JOIN and INNER JOIN

In the world of SQL, JOIN clause plays a key role in merging data from multiple tables. However, with JOIN and INNER JOIN, a question arises: are they really interchangeable? Let’s take a deeper look at both structures to reveal their similarities and nuances.

Functionally speaking, JOIN and INNER JOIN are indeed equivalent. Both statements produce the same result set by filtering the rows in the specified table based on the specified join conditions. In the example provided, they will both return the same rows, where the table.ID column in the table equals the otherTable.FK column in the otherTable.

In most cases, the performance impact of these connections is negligible. However, some SQL implementations may exhibit subtle differences in their optimization techniques for JOIN and INNER JOIN. However, these differences are often insignificant and difficult to detect in real scenarios.

The advantage of INNER JOIN is its readability. By explicitly specifying "INNER" you can more clearly indicate that you intend to perform a join that contains only rows that satisfy the join criteria. This clarity is especially beneficial when dealing with complex queries involving multiple join types such as LEFT JOIN or RIGHT JOIN.

So while JOIN and INNER JOIN are functionally equivalent, INNER JOIN has the advantage of enhanced clarity. This is especially important when using connection types other than INNER, as it explicitly states the desired behavior. Therefore, even if the performance impact is negligible, INNER JOIN is still the first choice to improve code readability and maintainability.

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