Django 重复SYNCDB会产生不同的结果？

当我运行

syncdb

时，它给了我一个

MySQL 150

错误，可能与FK有关。但是，当我反复运行

syncdb

时，它最终会工作（下面的整个跟踪）。为什么会发生这种情况

    david-MacBook-Pro$ syncdb
    Creating tables ...
    Creating table jobs_company
    Creating table jobs_job
    Traceback (most recent call last):
      File "manage.py", line 14, in <module>
        execute_manager(settings)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 438, in execute_manager
        utility.execute()
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 379, in execute
        self.fetch_command(subcommand).run_from_argv(self.argv)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 191, in run_from_argv
        self.execute(*args, **options.__dict__)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 220, in execute
        output = self.handle(*args, **options)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 351, in handle
        return self.handle_noargs(**options)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/commands/syncdb.py", line 101, in handle_noargs
        cursor.execute(statement)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/util.py", line 34, in execute
        return self.cursor.execute(sql, params)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 86, in execute
        return self.cursor.execute(query, args)
      File "build/bdist.macosx-10.6-intel/egg/MySQLdb/cursors.py", line 174, in execute
      File "build/bdist.macosx-10.6-intel/egg/MySQLdb/connections.py", line 36, in defaulterrorhandler
    _mysql_exceptions.OperationalError: (1005, "Can't create table 'david542.#sql-2c3_57e' (errno: 150)")
    david-MacBook-Pro:$ syncdb
    Creating tables ...
    Creating table jobs_jobposition
    Creating table jobs_externaljob
    Creating table jobs_externalsite
    Creating table jobs_sitevisit
    Traceback (most recent call last):
      File "manage.py", line 14, in <module>
        execute_manager(settings)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 438, in execute_manager
        utility.execute()
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 379, in execute
        self.fetch_command(subcommand).run_from_argv(self.argv)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 191, in run_from_argv
        self.execute(*args, **options.__dict__)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 220, in execute
        output = self.handle(*args, **options)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 351, in handle
        return self.handle_noargs(**options)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/commands/syncdb.py", line 101, in handle_noargs
        cursor.execute(statement)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/util.py", line 34, in execute
        return self.cursor.execute(sql, params)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 86, in execute
        return self.cursor.execute(query, args)
      File "build/bdist.macosx-10.6-intel/egg/MySQLdb/cursors.py", line 174, in execute
      File "build/bdist.macosx-10.6-intel/egg/MySQLdb/connections.py", line 36, in defaulterrorhandler
    _mysql_exceptions.OperationalError: (1005, "Can't create table 'david542.#sql-2c3_57f' (errno: 150)")
    david-MacBook-Pro$ syncdb
    Creating tables ...
    Creating table jobs_application
    Traceback (most recent call last):
      File "manage.py", line 14, in <module>
        execute_manager(settings)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 438, in execute_manager
        utility.execute()
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 379, in execute
        self.fetch_command(subcommand).run_from_argv(self.argv)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 191, in run_from_argv
        self.execute(*args, **options.__dict__)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 220, in execute
        output = self.handle(*args, **options)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py", line 351, in handle
        return self.handle_noargs(**options)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/commands/syncdb.py", line 101, in handle_noargs
        cursor.execute(statement)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/util.py", line 34, in execute
        return self.cursor.execute(sql, params)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 86, in execute
        return self.cursor.execute(query, args)
      File "build/bdist.macosx-10.6-intel/egg/MySQLdb/cursors.py", line 174, in execute
      File "build/bdist.macosx-10.6-intel/egg/MySQLdb/connections.py", line 36, in defaulterrorhandler
    _mysql_exceptions.OperationalError: (1005, "Can't create table 'david542.#sql-2c3_580' (errno: 150)")
    david-MacBook-Pro$ syncdb
    Creating tables ...
    Installing custom SQL ...
    Installing indexes ...
    No fixtures found.

david MacBook Pro$syncdb
正在创建表。。。
创建table jobs\u公司
创建表作业\u作业
回溯（最近一次呼叫最后一次）：
文件“manage.py”，第14行，在
执行\u管理器（设置）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/__init__.py”，第438行，在execute_manager中
utility.execute（）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/_init___;.py”，第379行，在execute中
self.fetch_命令（子命令）。从_argv（self.argv）运行_
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py”，第191行，运行时从_argv开始
self.execute（*args，**选项._dict__;
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/base.py”，第220行，在execute中
输出=self.handle（*args，**选项）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/base.py”，第351行，在handle中
返回self.handle\u noargs（**选项）
handle_noargs中的文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/commands/syncdb.py”，第101行
cursor.execute（语句）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/db/backends/util.py”，执行中的第34行
返回self.cursor.execute（sql，params）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/db/backends/mysql/base.py”，执行中的第86行
返回self.cursor.execute（查询，参数）
文件“build/bdist.macosx-10.6-intel/egg/MySQLdb/cursors.py”，执行中第174行
文件“build/bdist.macosx-10.6-intel/egg/MySQLdb/connections.py”，第36行，在defaulterrorhandler中
_mysql_exceptions.OperationalError:（1005，“无法创建表'david542.#sql-2c3_57e'（错误号：150）”）
david MacBook Pro:$syncdb
正在创建表。。。
创建表jobs\u jobsposition
创建表作业\u外部作业
创建表作业\u外部站点
创建表作业\u SiteVisite
回溯（最近一次呼叫最后一次）：
文件“manage.py”，第14行，在
执行\u管理器（设置）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/__init__.py”，第438行，在execute_manager中
utility.execute（）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/_init___;.py”，第379行，在execute中
self.fetch_命令（子命令）。从_argv（self.argv）运行_
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py”，第191行，运行时从_argv开始
self.execute（*args，**选项._dict__;
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/base.py”，第220行，在execute中
输出=self.handle（*args，**选项）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/base.py”，第351行，在handle中
返回self.handle\u noargs（**选项）
handle_noargs中的文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/commands/syncdb.py”，第101行
cursor.execute（语句）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/db/backends/util.py”，执行中的第34行
返回self.cursor.execute（sql，params）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/db/backends/mysql/base.py”，执行中的第86行
返回self.cursor.execute（查询，参数）
文件“build/bdist.macosx-10.6-intel/egg/MySQLdb/cursors.py”，执行中第174行
文件“build/bdist.macosx-10.6-intel/egg/MySQLdb/connections.py”，第36行，在defaulterrorhandler中
_mysql_exceptions.OperationalError:（1005，“无法创建表'david542.#sql-2c3_57f'（错误号：150）”）
david MacBook Pro$syncdb
正在创建表。。。
在应用程序中创建表作业
回溯（最近一次呼叫最后一次）：
文件“manage.py”，第14行，在
执行\u管理器（设置）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/__init__.py”，第438行，在execute_manager中
utility.execute（）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/_init___;.py”，第379行，在execute中
self.fetch_命令（子命令）。从_argv（self.argv）运行_
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/base.py”，第191行，运行时从_argv开始
self.execute（*args，**选项._dict__;
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/base.py”，第220行，在execute中
输出=self.handle（*args，**选项）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/base.py”，第351行，在handle中
返回self.handle\u noargs（**选项）
handle_noargs中的文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/core/management/commands/syncdb.py”，第101行
cursor.execute（语句）
文件“/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site packages/django/db/backends/util.py”，第34行，在execu中