SQL INNER JOIN syntax

Question

the two bits of SQL below get the same result

SELECT c.name, o.product  
FROM customer c, order o  
WHERE c.id = o.cust_id  
AND o.value = 150  

SELECT c.name, o.product  
FROM customer c  
INNER JOIN order o on c.id = o.cust_id  
WHERE o.value = 150

I've seen both styles used as standard at different companies. From what I've seen, the 2nd one is what most people recommend online. Is there any real reason for this other than style? Does using an Inner Join sometimes have better performance?

I've noticed Ingres and Oracle developers tend to use the first style, whereas Microsoft SQL Server users have tended to use the second, but that might just be a coincidence.

Thanks for any insight, I've wondered about this for a while.

Edit: I've changed the title from 'SQL Inner Join versus Cartesian Product' as I was using the incorrect terminlogy. Thanks for all the responses so far.

Answer 1

Both queries are an inner joins and equivalent. The first is the older method of doing things, whereas the use of the JOIN syntax only became common after the introduction of the SQL-92 standard (I believe it's in the older definitions, just wasn't particularly widely used before then).

The use of the JOIN syntax is strongly preferred as it separates the join logic from the filtering logic in the WHERE clause. Whilst the JOIN syntax is really syntactic sugar for inner joins it's strength lies with outer joins where the old * syntax can produce situations where it is impossible to unambiguously describe the join and the interpretation is implementation-dependent. The [LEFT | RIGHT] JOIN syntax avoids these pitfalls, and hence for consistency the use of the JOIN clause is preferable in all circumstances.

Note that neither of these two examples are Cartesian products. For that you'd use either

SELECT c.name, o.product   FROM customer c, order o   WHERE o.value = 150   

or

SELECT c.name, o.product   FROM customer c  CROSS JOIN order o  WHERE o.value = 150 

Answer 2

To answer part of your question, I think early bugs in the JOIN ... ON syntax in Oracle discouraged Oracle users away from that syntax. I don't think there are any particular problems now.

They are equivalent and should be parsed into the same internal representation for optimization.