TSQL — Does ordering of on clause matter

Question

For the simplified query:

Select t1.c1, t1.c2, t2.d1
FROM table1 t1
LEFT JOIN table2 t2
ON
(t1.c1 = t2.d2)

It seems from math by the symmetric property that this would be exactly the same as if one reversed the ON to:

Select t1.c1, t1.c2, t2.d1
FROM table1 t1
LEFT JOIN table2 t2
ON
(t2.d2 = t1.c1)

Is this always to true in TSQL or is there some exception where one could get more rows if the query was subtly changed as described above?

I've learned that very subtle join changes (in queries much more complicated than this simple example) can affect row counts greatly.

Also, in addition to rows returned (which I think should be EXACTLY THE SAME for both queries always) I would suppose that one ordering of the "ON" clause could make the query have better performance speed. Could someone verify that?

Answer 1

The ON condition in any sort of JOIN can be commutative, as you have observed. You can do ON a = b or ON b = a and have them mean precisely the same thing. They're nothing but Boolean expressions.