根据相关 table 更新 HSQL table 值

Question

我有 2 个相关表："Universities"(id, num_courses) 和 "Courses" (id, university_id)。我需要 University.num_courses 来表示 COUNT 门课程。

我可以查询我需要的数据：

SELECT 
Universities.id,
COUNT(Courses.university_id) as NumCourses
FROM Courses
JOIN Universities ON Universities.id = Courses.university_id
GROUP BY Universities.id

我如何用它更新大学？可以自动完成吗？

Answer 1

我不确定这就是你所说的 "automatically," 的意思，但可以通过循环来完成：

Sub UpdateUniversities
    Context = CreateUnoService("com.sun.star.sdb.DatabaseContext")
    databaseURLOrRegisteredName = "file:///C:/Users/JimStandard/Desktop/New Database.odb"
    Db = Context.getByName(databaseURLOrRegisteredName )
    Conn = Db.getConnection("","") 'username & password pair - HSQL default blank
    Stmt = Conn.createStatement()
    strSQL = "SELECT Universities.id, " & _
        "COUNT(Courses.university_id) as NumCourses " & _
        "FROM Courses " & _
        "JOIN Universities ON Universities.id = Courses.university_id " & _
        "GROUP BY Universities.id"
    oResult = Stmt.executeQuery(strSQL)
    Do While oResult.next()
        university_id = oResult.getLong(1)
        num_courses = oResult.getLong(2)
        Stmt = Conn.createStatement()
        strSQL = "UPDATE ""Universities"" SET ""num_courses"" = " & _
            num_courses & " WHERE ""id"" = " & university_id
        Stmt.executeUpdate(strSQL)
    Loop
    Conn.close()
End Sub

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