数据库技术之存储过程设计与实现(二)
原创性申明 此博文的出处 为 http://blog.csdn.net/zhujunxxxxx/article/details/39251353如果进行转载请注明出处。本文作者原创，邮箱zhujunxxxxx@163.com，如有问题请联系作者 存储过程的生成流程图 在上一篇的文章中我们知道了由一个存储过程的语句生成一
原创性申明
此博文的出处 为 http://blog.csdn.net/zhujunxxxxx/article/details/39251353如果进行转载请注明出处。本文作者原创，邮箱zhujunxxxxx@163.com，如有问题请联系作者
存储过程的生成流程图
在上一篇的文章中我们知道了由一个存储过程的语句生成一个语法树，但是这个语法树的保存在数据库系统中，这里给出一个存储过程的存储方案
可以看出存储过程的原来的sql语句是保存在一张表里面的。并且也把存储过程的语法树保存在了内存中，方便执行，不用再次编译了。
存储过程的执行流程图
在得到了语法树过后怎么执行这才是关键的。我们为了降低系统的耦合，原来系统中有的功能呢我们就不在去实现了，就利用系统自带的，存储过程是一个过程性的语言，必然有很多的计算，为了降低系统的复杂度，我么们需要把存储过程中遇到的表达式全部交有数据库引擎去执行，我们存储过程中嵌入的sql语句也交给了数据库引擎来执行。
这样的话我们就可以不用考虑sql语句的处理。降低了耦合度，也提高了逻辑难度。
我给出的这个流程图并没有包括所有的执行分支，反正具体的执行流程就是这样子的，然后其中没一个节点的处理方法也是有的
这一部分我是参照postgresql数据库的做法来做的
运行中的变量作用域
在存储过程执行的过程中有的的变量的作用范围是全局，有的范围是局部，解决这一问题的方法就是使用栈的数据结构来保存变量，这个数据结构我在上一篇文章中有给出来
这个是一篇论文中给的一副图，不过我的堆栈式用的Map来做，这样便于查找，没次查找变量的时候就从当前层找，找不到在往上一层找。这个数据结构就很好的解决了变量作用域的问题
此博文的出处 为 http://blog.csdn.net/zhujunxxxxx/article/details/39251353如果进行转载请注明出处。本文作者原创，邮箱zhujunxxxxx@163.com，如有问题请联系作者
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