如果连接列上不存在索引，那么优化器将选择动态哈希连接。

The optimizer will choose dynamic hash join if none of the joined columns has index.

youdao

哈希连接通常比分类合并连接快，因为它没有涉及到分类操作。

A hash join is usually faster than a sort merge join since there is no sort operation involved.

youdao

最常用的连接方法就是嵌套循环连接、分类合并连接和动态哈希连接。

The most commonly used join methods are nested-loop join, sort merge join and dynamic hash join.

youdao