如何通過笛卡爾乘積查詢追加表中不存在的記錄？

Question

我當前的查詢從2個表中返回所有可能的結果，並將它們插入聯結表中。

我當前的查詢如下所示：

INSERT INTO tblJunction_Courses_Software ( CourseID, SoftwareID )
SELECT tblCourses.CourseID, tblSoftware.SoftwareID
FROM tblSoftware, tblCourses
WHERE (((tblSoftware.Exclude)=No));

如何添加一個附加子句以確保每次運行查詢時都不會重復數據？

Answer 1

我認為您可以使用not exists子句來完成您想要的事情：

INSERT INTO tblJunction_Courses_Software ( CourseID, SoftwareID )
     SELECT c.CourseID, s.SoftwareID
     FROM tblSoftware as s CROSS JOIN tblCourses as c
     WHERE s.Exclude = No AND
           NOT EXISTS (SELECT 1
                       FROM tblJunction_Courses_Software as cs
                       WHERE cs.CourseId = c.CourseId AND
                             cs.SoftwareId = s.SOftwareId
                      );