JOIN ORDER OPTIMIZATION IN A QUERY OPTIMIZER FOR QUERIES WITH OUTER AND/OR SEMI JOINS

摘要

A system and method for join order optimization in a query optimizer is disclosed. The method includes receiving a query having a plurality of join operators, including at least one multi-way join between relational operators in the query tree. The join operators include at least one outer-join and/or semi-join. The multi-way-join is transformed to a multi-join operator with a plurality of join back bone children representing the relational operators. The dependencies that occur between the join back bone children are tracked. Join order validity is evaluated based on the tracked dependencies. One or more multi-join rules are applied to the multi-join operator sufficient to generate at least one join subtree when at least one join subtree is determined to have a valid join order.