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。

youdao

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。

youdao

The values of the inner data set's parameters are from the link table's SOURCE_ITEMID column because a work item can find its sub - work item's WI_ITEMID by retrieving the data from Links table.

内部数据参数的值来自于联系表格的source_itemid列，因为一个工作项可以通过从Links表格中获得数据，来找到其子工作项的WI_ITEMID。

youdao