Join Order Selection

Joins are associative so $R\bowtie S\bowtie T\bowtie U$ are equivalent to

1. $((R\bowtie S)\bowtie T)\bowtie U$
2. $(R\bowtie S)\bowtie (T\bowtie U)$
3. $R\bowtie (S\bowtie (T\bowtie U))$

→ Try to minimize the intermediate result
Need to decide which of the subexpressions is evaluated first

• Try to join with filtered one first