JOIN vs. WHERE: Which is Faster for Database Queries with Foreign Key Relationships?

JOIN vs. WHERE: Which is Faster for Database Queries?

In the world of database querying, speed is crucial. When you have two tables linked by a foreign key, such as Document and DocumentStats, you may wonder whether using a JOIN or WHERE clause is faster for retrieving data.

Question:

Consider the following query:

SELECT *
FROM Document, DocumentStats
WHERE DocumentStats.Id = Document.Id
  AND DocumentStats.NbViews > 500

An alternative query using an INNER JOIN is:

SELECT *
FROM Document
INNER JOIN DocumentStats ON Document.Id = DocumentStats.Id
WHERE DocumentStats.NbViews > 500

Which query executes faster, or are they equivalent?

Answer:

Theoretically, both queries should execute equally fast as the query optimizer optimizes the execution plan. However, in practice, the database engine may produce better execution plans for one of the queries, especially for more complex operations.

In short, it's best to test both queries on your database engine to determine which one performs better. However, you can generally expect them to have comparable speeds for simple queries.

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