Question

Consider the example from MSDN documentation:

SELECT p.Name, pr.ProductReviewID
FROM Production.Product p
LEFT OUTER JOIN Production.ProductReview pr
ON p.ProductID = pr.ProductID

In this example, it is clear that the table on the left is “Production” and that is where all rows will be returned from, and then only those that match in ProductReview.

But now consider the following hypothetical query with 3 tables A,B,C

select * from A
inner Join B on A.field1 = B.field1
left outer join C on C.field2 = b.Field2

Which is the left table in this query (from which all records will be returned, regardless of a match to C)? Is it A or B? Or is it the result of the join from A & B?

My confusion arises from the following MSDN documentation, which states that “Outer joins can be specified in the FROM clause only” which would mean that the left table in my hypothetical query is A, but then I dont have an ON clause that specifies the join condition – in which case is my hypothetical query a bad one?

Answer 1

Since there is an INNER JOIN between A and B, only rows from B that match A will qualify for the LEFT JOIN to C.