关于SQL中left join的一些坑

最近写了一个十分复杂的SQL语句,涉及到了很多表的left join操作。最终的SQL语句执行速度惊人的慢,即使加了索引并且让大部分查询命中也会是一个难以忍受的等待时间。偶然间发现,本该为1000多条的结果居然实际是16万条。后来发现这种情况会出现在有一对多产生匹配时出现。
(暂且占个坑,以后补充)

macOS上Word 2016里使用MathType特殊字符显示方框问题

MathType打公式显示方框一般是字体问题导致的。不过像mt extra字体有好多版本,与MathType版本不兼容的话还是不能解决问题。MathType使用到的字体可以点击这里查看
不过尽管知道哪些字体,安装后经常还是不行。通过与WIRIS公司的技术支持联系后,得到了一个可行的方案:

  1. 进入 应用程序 > MathType > Fonts > TrueType目录
  2. 把下面的字体挨个安装一遍。一些字体会出现警告,直接选择确认
  3. 如果依然不起作用,重启电脑
  4. 常规重启无效的话,尝试重启开机时按住Shift键。见到苹果logo后松手。这时系统会进入安全模式。

以下是邮件回复原文

Hello,

Most of the symbols that you're looking for come from the Symbol font. The MathType application installs the fonts during the standard installation of the software. Since the fonts aren't properly working, let's take a look at the fonts in the MathType folder.

Applications > MathType > Fonts > TrueType

You can find Symbol and MT Extra, and double-click on each of them (one at a time) and install them manually from here. It usually will take you to a font validation window, and give you a warning. Proceed despite the standard warning to install them. After you have done so, you can test again. 

If it doesn't clear up the issue, you should try booting up the computer in safe mode. After doing so, you can re-boot in regular mode. This should also clear the font cache and clear the issue. To boot in safe mode, you can press and hold the "Shift" key when you hear the startup tone. You can release the "Shift" key after the Apple logo appears.