图8展示了如果规则使用了多个参考列，那么左外部连接就进行级联。

Figure 8 shows that the left outer join operations are cascaded if a rule USES more than one reference column.

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图8展示了如果规则使用了多个参考列，那么左外部连接就进行级联。

Figure 8 shows that the left outer join operations are cascaded if a rule USES more than one reference column.

youdao