SQL left join vs multiple tables on FROM line?

Question

Most SQL dialects accept both the following queries:

SELECT a.foo, b.foo
FROM a, b
WHERE a.x = b.x

SELECT a.foo, b.foo
FROM a
LEFT JOIN b ON a.x = b.x
         


        

Answer 1

The second is preferred because it is far less likely to result in an accidental cross join by forgetting to put inthe where clause. A join with no on clause will fail the syntax check, an old style join with no where clause will not fail, it will do a cross join.

Additionally when you later have to a left join, it is helpful for maintenance that they all be in the same structure. And the old syntax has been out of date since 1992, it is well past time to stop using it.

Plus I have found that many people who exclusively use the first syntax don't really understand joins and understanding joins is critical to getting correct results when querying.