| 摘要 |
Techniques are provided for determining query cost for a query that include an outer query and at least a first subquery. The techniques include determining a filtering factor for the first subquery based on a first cardinality and a second cardinality. The first cardinality is determined based on a first set of query blocks in the query. The second cardinality is determined based on a second set of query blocks. The first set of query blocks includes the outer query and zero or more subqueries from the query and does not include the first subquery. The second set of query blocks includes all the query blocks in the first set of query blocks and, in addition, the first subquery. The techniques also include determining a cost for the query based, at least, on the filtering factor for the first subquery.
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