Start from the leftmost deepest operator, in this case, the OUTER of NLJOIN ( 2) which is TBSCAN ( 2), and the INNER which is TBSCAN ( 4), and then the join predicate itself which is NLJOIN ( 2). 从最左侧、最深的操作开始,在这里就是NLJOIN(2)的OUTER即TBSCAN(2),然后INNER即TBSCAN(4),最后是连接断言本身即NLJOIN(2)。