parenthetic grouping of join clauses

What is the difference between these joins? 1. a left join b left join c 2. (a left join b) left join c 3. a left join (b left join c) Does the grouping only affect the order of the joins? Will the query engine decompose #1 into one of #2 or #3, i.e. pick an order for doing the joins? I'm asking because h2 uses indexes on c for #1, but for #2 does a table scan of c. Here b is a simple many-to-many join table with columns (a_id, c_id).