在 SQL Server 2008 中将默认值插入到 MANY-TO-MANY 关系的脚本

Question

我正在使用SQL Server 2008。请考虑以下表格：

表学生

╔════╦═══════════╦══════════╗
║ ID ║ FIRSTNAME ║ LASTNAME ║
╠════╬═══════════╬══════════╣
║  1 ║ joe       ║ Smith    ║
║  2 ║ frank     ║ Smith    ║
║  3 ║ Scott     ║ Smith    ║
╚════╩═══════════╩══════════╝

表课程

╔════╦═════════╦════════════════╗
║ ID ║  NAME   ║  DESCRIPTION   ║
╠════╬═════════╬════════════════╣
║  1 ║ Physics ║ PHYSICS COURSE ║
║  2 ║ MATH    ║ COURSE         ║
╚════╩═════════╩════════════════╝

表格STUDENT_COURSE

╔════════════╦═══════════╦═══════╗
║ STUDENT_ID ║ COURSE_ID ║ GRADE ║
╠════════════╬═══════════╬═══════╣
║          1 ║         1 ║     9 ║
║          2 ║         1 ║     8 ║
║          3 ║         1 ║     6 ║
╚════════════╩═══════════╩═══════╝

如果该用户不存在这样的成绩，我需要为所有用户插入数学课程的默认成绩 10。

我不熟悉 Microsoft SQL Server 和 T-SQL。你能帮我解决这样的问题吗？

Answer 1

INSERT INTO STUDENT_COURSE (Student_ID, course_ID, grade)
SELECT  a.ID as StudentID, b.ID as Course_ID, 10 AS grade
FROM    Student a 
        CROSS JOIN Course b
        LEFT JOIN 
        (
            SELECT  d.*
            FROM    STUDENT_COURSE d
                    INNER JOIN Course e
                        ON d.Course_ID = e.ID
            WHERE   e.Name = 'Math'
        ) c ON  a.ID = c.student_ID AND
                b.ID = c.course_ID 
WHERE   c.student_ID IS NULL AND 
        b.Name = 'Math'

• SQLFiddle Demo
• SQLFiddle Demo (added record which one student has already grade on MATH)

如果您列出表 STUDENT_COURSE 上的所有记录，则输出

MySQL> SELECT * FROM STUDENT_COURSE

╔════════════╦═══════════╦═══════╗
║ STUDENT_ID ║ COURSE_ID ║ GRADE ║
╠════════════╬═══════════╬═══════╣
║          1 ║         1 ║     9 ║
║          2 ║         1 ║     8 ║
║          3 ║         1 ║     6 ║
║          1 ║         2 ║    10 ║
║          2 ║         2 ║    10 ║
║          3 ║         2 ║    10 ║
╚════════════╩═══════════╩═══════╝