将不同表中的多条记录组合成一个字符串答案

【问题标题】：Combining multiple records from different tables into one string将不同表中的多条记录组合成一个字符串
【发布时间】：2020-06-29 20:44:29
【问题描述】：

我正在尝试使用 studentID 从一个表中获取他们的名字和姓氏，然后使用 HomeworkID 获取他们的一个家庭作业的结果，并使用 tkinter 将结果显示在列表框小部件中。但是，在它可以显示之前，我首先需要能够获取数据。这是我到目前为止所拥有的：

 def viewresults (self, sethw):

        print (self.Homework_To_Set.get())
        #resultslist = []
        conn = sqlite3.connect('MyComputerScience.db')
        c = conn.cursor()
        homeworkID = c.execute("SELECT HWID FROM HomeworkInfo WHERE HomeworkName = ?", (self.Homework_To_Set.get(), )).fetchone()
        studentsnamecheck = c.execute("SELECT StudentID FROM HomeworkSet WHERE  HWID = ?", ((homeworkID[0], ))).fetchall()
        if len(studentsnamecheck) == 0:
            self.View_Results.insert(END, "No one has completed this homework!")
        else:
            for x in studentsnamecheck:
                c.execute("SELECT FName || ' ' || SName FROM users WHERE UserID = ?", (str(x), ))
                res1 = (c.fetchall())
                for i in (studentsnamecheck):
                    result_collect = c.execute("SELECT Results FROM HomeworkSet WHERE StudentID = ? AND HWID = ?", ((str(i)), self.Homework_To_Set.get() ))

                var_insert_results = ((res1), (result_collect))
                self.View_Results.insert(END, str(var_insert_results))

这是当前的输出：

([], <sqlite3.Cursor object at 0x000001F40E1809D0>)
([], <sqlite3.Cursor object at 0x000001F40E1809D0>)
([], <sqlite3.Cursor object at 0x000001F40E1809D0>)
([], <sqlite3.Cursor object at 0x000001F40E1809D0>)
([], <sqlite3.Cursor object at 0x000001F40E1809D0>)
([], <sqlite3.Cursor object at 0x000001F40E1809D0>)
([], <sqlite3.Cursor object at 0x000001F40E1809D0>)

这是数据库的架构：

c.execute("""CREATE TABLE IF NOT EXISTS users (
            UserID INTEGER PRIMARY KEY AUTOINCREMENT,
            FName text,
            SName text,
            username text,
            password text,
            userType text,
            ClassName text);""")

c.execute("""CREATE TABLE IF NOT EXISTS ClassInfo (
            ClassID INTEGER PRIMARY KEY AUTOINCREMENT,
            ClassName text,
            Teacher text);""")

c.execute("""CREATE TABLE IF NOT EXISTS HomeworkInfo (
            HWID INTEGER PRIMARY KEY,
            HomeworkName text);""")


c.execute("""CREATE TABLE IF NOT EXISTS HomeworkSet (
            HWID integer,
            StudentID text,
            Results text,
            FOREIGN KEY (StudentID) REFERENCES users(UserID)
            FOREIGN KEY (HWID) REFERENCES HomeworkInfo(HWID));""")

【问题讨论】：

"current output: ... ：你必须再次循环生成的.Cursor object
您可以使用SQL JOIN 来组合三个SELECT 语句，这样您就可以使用一个for 循环来遍历结果。

标签： python sqlite tkinter

【解决方案1】：

您的代码中有几个问题：

c.execute("SELECT FName || ' ' || SName FROM users WHERE UserID = ?", (str(x), ))
res1 = (c.fetchall())
for i in (studentsnamecheck):
    result_collect = c.execute("SELECT Results FROM HomeworkSet WHERE StudentID = ? AND HWID = ?",
                               ((str(i)), self.Homework_To_Set.get() ))

users 表中没有UserID 字段；可能是username
str(x) 应该是 x[0]
应该循环通过res1 而不是studentsnamecheck
str(i) 应该是 x[0]
self.Homework_To_Set.get() 应该是 homeworkID[0]

所以代码应该是：

def viewresults(self, sethw):
    print(self.Homework_To_Set.get())
    conn = sqlite3.connect('MyComputerScience.db')
    c = conn.cursor()
    homeworkID = c.execute("SELECT HWID FROM HomeworkInfo WHERE HomeworkName = ?",
                           (self.Homework_To_Set.get(),)).fetchone()
    studentsnamecheck = c.execute("SELECT StudentID FROM HomeworkSet WHERE HWID = ?",
                                  (homeworkID[0],)).fetchall()
    if len(studentsnamecheck) == 0:
        self.View_Results.insert(END, "No one has completed this homework!")
    else:
        for x in studentsnamecheck:
            c.execute("SELECT FName||' '||SName FROM users WHERE username = ?", (x[0],))
            res1 = c.fetchall()
            for i in res1:
                results = c.execute("SELECT Results FROM HomeworkSet WHERE StudentID = ? AND HWID = ?",
                                    (x[0], homeworkID[0])).fetchone()
                self.View_Results.insert(END, '%-30s  %s'%(i[0], results[0]))

但是，您可以将SELECT 语句组合成一个查询：

def viewresults(self, sethw):
    conn = sqlite3.connect('MyComputerScience.db')
    c = conn.cursor()
    sql = """
        SELECT SName||' '||FName, Results
        FROM HomeworkSet, HomeworkInfo, users
        WHERE HomeworkInfo.HomeworkName = ?
          AND HomeworkInfo.HWID = HomeworkSet.HWID
          AND HomeworkSet.StudentID = users.username
    """
    c.execute(sql, (self.Homework_To_Set.get(),))
    for result in c:
        self.View_Results.insert(END, '%-30s  %s'%result)

【讨论】：