在 Python 3.4 中在 MySQL 中创建表答案

【问题标题】：Creating tables in MySQL in Python 3.4在 Python 3.4 中在 MySQL 中创建表
【发布时间】：2016-05-22 09:51:13
【问题描述】：

我在 Windows 10 上使用 Python 3.4 作为 cgi 和 MySQL 数据库服务器通过 Apache 运行服务器。当我尝试运行用于创建数据库的函数时，出现错误：

DatabaseError: 1005 (HY000): Can't create table `testdb`.`studentexam` (errno: 150 
"Foreign key constraint is incorrectly formed")

创建数据库的函数

import mysql.connector as conn

#connect to server
db=conn.connect(host="localhost",user="root",password="")
cursor=db.cursor()
#create database
cursor.execute("""CREATE DATABASE IF NOT EXISTS Testdb""")
db.commit()
#use database
cursor.execute("""USE Testdb""")
db.commit()
#create Teacher table
cursor.execute("""CREATE TABLE IF NOT EXISTS Teacher(
    TeacherUsername VARCHAR(255) PRIMARY KEY,
    TeacherPassword TEXT)""")
db.commit()
#create student table
cursor.execute("""CREATE TABLE IF NOT EXISTS Student(
    StudentNo INT PRIMARY KEY,
    StudentSurname TEXT,
    StudentForename TEXT,
    StudentTeacher VARCHAR(255),
    StudentPassword TEXT,
    FOREIGN KEY(StudentTeacher) REFERENCES Teacher(TeacherUsername))""")
db.commit()
#create exam table
cursor.execute("""CREATE TABLE IF NOT EXISTS Exam(
    TestName VARCHAR(255) PRIMARY KEY,
    TestTotalMarks TEXT,
    Teacher VARCHAR(255),
    FOREIGN KEY(Teacher) REFERENCES Teacher(TeacherUsername))""")
db.commit()
#create StudentExam table
cursor.execute("""CREATE TABLE IF NOT EXISTS StudentExam(
    TestName VARCHAR(255),
    StudentID INT,
    StudentTotalMarks INT,
    PRIMARY KEY(TestName,StudentID),
    FOREIGN KEY(TestName) REFERENCES Exam(TestName),
    FOREIGN KEY(StudentID) REFERENCES Student(StudentID))""")
db.commit()
#create ExamSection table
cursor.execute("""CREATE TABLE IF NOT EXISTS ExamSection(
    TestName VARCHAR(255),
    SectionID INT,
    PRIMARY KEY(TestName,SectionID),
    FOREIGN KEY(TestName) REFERENCES Exam(TestName),
    FOREIGN KEY(SectionID) REFERENCES Section(SectionID))""")
db.commit()
#create Section table
cursor.execute("""CREATE TABLE IF NOT EXISTS Section(
    SectionID INT PRIMARY KEY,
    SectionName TEXT,
    SectionTotalMarks INT)""")
db.commit()
#create Question table
cursor.execute("""CREATE TABLE IF NOT EXISTS Question(
    QuestionID INT PRIMARY KEY,
    SectionID VARCHAR(255),
    Image TEXT,
    Question TEXT,
    PossibleAnswer TEXT,
    CorrectAnswer TEXT,
    QuestionType TEXT,
    FOREIGN KEY(SectionID) REFERENCES Section(SectionID))""")
db.commit()
#create QuestionResults Table
cursor.execute("""CREATE TABLE IF NOT EXISTS QuestionResults(
    QuestionID INT,
    StudentID INT,
    SectionID VARCHAR(255),
    StudentAnswer TEXT,
    PRIMARY KEY(QuestionID,StudentID),
    FOREIGN KEY(QuestionID) REFERENCES Question(QuestionID)
    FOREIGN KEY(StudentID) REFERENCES Student(StudentID))""")
db.commit()
#create Revision table
cursor.execute("""CREATE TABLE IF NOT EXISTS Revision(
    RevisionID INT PRIMARY KEY,
    RevisionSheet TEXT,
    TeacherUsername VARCHAR(255),
    FOREIGN KEY(TeacherUsername) REFERENCES Teacher(TeacherUsername))""")
db.commit()
#create StudentRevition table
cursor.execute("""CREATE TABLE IF NOT EXISTS StudentRevision(
    RevisionID INT,
    StudentID INT,
    PRIMARY KEY(RevisionID,StudentID),
    FOREIGN KEY(RevisionID) REFERENCES Revision(RevisionID),
    FOREIGN KEY(StudentID) REFERENCES Student(StudentID))""")
db.commit()
#create StudentResults table
cursor.execute("""CREATE TABLE IF NOT EXISTS StudentResults(
    SectionID VARCHAR(255),
    StudentID INT,
    StudentSectionMarks INT,
    PRIMARY KEY(SectionID,StudentID),
    FOREIGN KEY(SectionID) REFERENCES Section(SectionID),
    FOREIGN KEY(StudentID) REFERENCES Student(StudentID))""")
db.commit()
cursor.close()

编辑：我将 StudentNo 更改为 StudentID，现在得到错误：

DatabaseError: 1005 (HY000): Can't create table `testdb`.`examsection` (errno: 150
"Foreign key constraint is incorrectly formed")

【问题讨论】：

你的代码比较乱，很难查。尝试将所有 SQL 语句收集到文件 .sql 中，并通过键入 \i name_file.sql 从 psql 命令行运行它。可能你会有更多的控制和更好的错误自省。顺便说一句，错误在 SQL 中而不是在 Python 代码中。

标签： python mysql cgi

【解决方案1】：

改变这个：

#create student table
cursor.execute("""CREATE TABLE IF NOT EXISTS Student(
StudentNo INT PRIMARY KEY,
StudentSurname TEXT,
StudentForename TEXT,
StudentTeacher VARCHAR(255),
StudentPassword TEXT,
FOREIGN KEY(StudentTeacher) REFERENCES Teacher(TeacherUsername))""")
db.commit()

到这里：

#create student table
cursor.execute("""CREATE TABLE IF NOT EXISTS Student(
StudentID INT PRIMARY KEY,
StudentSurname TEXT,
StudentForename TEXT,
StudentTeacher VARCHAR(255),
StudentPassword TEXT,
FOREIGN KEY(StudentTeacher) REFERENCES Teacher(TeacherUsername))""")
db.commit()

【讨论】：

【解决方案2】：

创建 StudentExam 时，您引用了不存在的 Student.StudentId。您似乎更愿意引用 Student.StudentNo。

编辑：

创建 ExamSection 时，您引用了尚不存在的 Section 表。将 Section 创建状态向上移动，以便它在您创建 ExamSection 之前运行并提交。

【讨论】：