轉自http://tolywang.itpub.net/post/48/384555

card是指計劃中這一步所處理的行數。 cost指cbo中這一步所耗費的資源，這個值是相對值。 bytes指cbo中這一步所處理所有記錄的位元組數，是估算出來的一組值

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Cost： The cost assigned to each step of the query plan by the CBO. The CBO works by generating many different execution paths/plans for the same query and assigns a cost to each and every one. The query plan with the lowest cost wins. In the full outer join example, we can see the total cost for this query is 10.

Card： Card is short for Cardinality. It is the estimated number of rows that will flow out of a given query plan step. In the full outer join example, we can see the optimizer expects there to be 327 rows in EMP and 4 rows in DEPT.

Bytes： The size in bytes of the data the CBO expects each step of the plan to return. This is dependent on the number of rows (Card) and the estimated width of the rows.

Oracle 執行計劃中一些引數的含義

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