If there is an index on the join column, the costs will be significantly less; otherwise the database server must perform table scans for all tables, both outer and inner tables.

如果连接列上有一个索引，那么其成本会相当低；否则，数据库服务器就必须对所有表(外部和内部表)执行表扫描。

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The join is performed by scanning the inner table of the hash join, CUSTOMERS, and generating a lookup table by hashing the join column values.

该连接的执行过程包括扫描散列连接中的内表CUSTOMERS，并通过散列连接列的值生成一个查找表。

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Select the inner table of links, and bind its TARGET_ITEMID column to the WI_ITEMID column of the outer table (Figure 15).

选择联系的内部表格，并将其TARGET _ itemid列于外层表格(图15)的wi_itemid列联系起来。

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