你想要 UPDATE FROM:

UPDATE N1
SET N1.is_last_child = 1
FROM Node N1
LEFT OUTER JOIN Node N2
    ON N1.ID = N2.Parent_ID
WHERE N2.ID IS NULL

左外连接在概念上与使用 NOT IN 相同，只是它更易于阅读并且您不需要一堆嵌套查询.

The left outer join is conceptually the same as using NOT IN only it's easier to read and you don't need a bunch of nested queries.