Question

Suppose I have two tables that are linked (one has a foreign key to the other):

CREATE TABLE Document (
  Id INT PRIMARY KEY,
  Name VARCHAR 255
)

CREATE TABLE DocumentStats (
  Id INT PRIMARY KEY,
  DocumentId INT, -- this is a foreign key to table Document
  NbViews INT
)

I know, this is not the smartest way of doing things, but this is the best example I could come up with.

Now, I want to get all documents that have more than 500 views. The two solutions that come to my mind are:

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

or:

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

Are both queries equivalent, or is there one way that is far better than the other? If so, why?

EDIT: as requested in the answers, this question was aimed at SQL Server, but I would be interested in knowing if it is different for other database engines (MySQL, etc…).

Answer 1

Theoretically, no, it shouldn’t be any faster. The query optimizer should be able to generate an identical execution plan. However, some database engines can produce better execution plans for one of them (not likely to happen for such a simple query but for complex enough ones). You should test both and see (on your database engine).