Re: In general, which of these queries would be faster?

[Apachez]

In 4.1 and earlier the

t1, t2 WHERE t1.id = t2.id

is exactly the same as

t1 INNER JOIN t2 ON (t1.id = t2.id)

However since 5.0 this has changed a bit.

The change is that the t1, t2 WHERE t1.id = t2.id method has now lower execution priority than the other joins in the query.

Example...

If you mix t1, t2 WHERE t1.id = t2.id with a couple of LEFT JOINs the optimizer would see that the t1, t2 is actually an INNER JOIN and by performance excute this one first and then the LEFT JOINs (or the other way around depending on which index might exist etc).

But from 5.0 LEFT JOIN will ALWAYS be executed before t1, t2 WHERE t1.id = t2.id method (or rather t1, t2 will be ALWAYS excuted AFTER proper joins).

So if you want to keep performance in 5.0 and upwards you "should" rewrite your t1, t2 joins into "proper" t1 INNER JOIN t2 joins (unless someone changes this again in future)...