用 JOIN/APPLY 替换子查询

Question

我有以下 SQL。

SELECT t0.QustionId, t1.QuestionText, t2.AnswerText FROM
ActiveQuestion AS t0
INNER JOIN Question AS t1
    ON t1.QuestionId = ActiveQuestion.QuestionId
LEFT OUTER JOIN Answer AS t2
    ON t2.SectionId = t0.SectionId
    AND t1.ParentId IN 
            (SELECT QuestionId 
                    FROM Question WHERE SharedQuestionId = t2.SharedQeustionId)

问题可以共享（使用相同的 SharedQuestionId），问题可以有父问题。

我想摆脱子查询。正确的做法是什么？

Answer 1

JOIN 表Question 再次使用不同的别名：

SELECT 
  t0.QustionId, 
  t1.QuestionText, 
  t2.AnswerText,
  p.questionI ParentQuestionId
FROM ActiveQuestion      AS t0
INNER JOIN Question      AS t1  ON t1.QuestionId      = ActiveQuestion.QuestionId
LEFT OUTER JOIN Answer   AS t2  ON t2.SectionId       = t0.SectionId
LEFT OUTER JOIN Question AS  p  ON t1.ParentId        = p.QuestionId 
                               AND p.SharedQuestionId = t2.SharedQeustionId;