MySQL的总UDF（用户定义函数）用C [英] mysql aggregate UDF (user defined function) in C

问题描述

我需要编写用于MySQL 5.x的一个聚合扩展功能（C实现）我已经走遍了文档（包括浏览SQL / udf_example.c），但我没有发现任何东西，是短暂的，给点意见，并表明我正是我需要做的。

I need to write an aggregate extension function (implemented in C) for mySQL 5.x. I have scoured the documentation (including browsing sql/udf_example.c) but I do not find anything that is brief, to the point and shows me just what I need to do.

这就是问题所在：

1. 我有一个C结构（美孚）



2. 我有一个C函数，它接受这些美孚结构的数组，执行一个操作，阵列上，并返回一个double。

1. I have a C struct (Foo)

2. I have a C function that takes an array of these Foo structs, performs an operation, on the array, and returns a double.

结构FooBar的{
  字符*日期;
  双周岁;
  双怀特;
  双倍工资;
  INT eye_color;
};

struct FooBar { char * date; double age; double wight; double salary; int eye_color; };

/ *处理功能的 /
双processFooBars（结构FooBar的的foobars，常量为size_t大小）;​​

/* Processing function / double processFooBars(struct FooBar foobars, const size_t size);

/ * MySQL表* /
CREATE TABLE foo_bar这样的名称（the_date DATE，双岁，双重量，双薪，INT eye_color};

/* MySQL table */ CREATE TABLE foo_bar( the_date DATE, double age, double weight, double salary, int eye_color};

我希望能够创造这样一个聚合函数：（我也许使用PostgreSQL语法）

I want to be able to create an aggregate function thus: (I maybe using PostgreSQL syntax)

CREATE凝聚函数proc_foobar RETURNS REAL SONAME myshlib.so ALIAS my_wrapper_func

CREATE AGGREGATE FUNCTION proc_foobar RETURNS REAL soname myshlib.so ALIAS my_wrapper_func

然后我就可以在MySQL查询使用这样的：

I can then use it in a MySQL Query thus:

选择proc_foobar（）作为喜爱程度从foo_bar这样WHERE the_date'1-JAN-09和1日 - 12月09'之间。

SELECT proc_foobar() as likeability FROM foo_bar WHERE the_date BETWEEN '1-Jan-09' and '1-Dec-09'

这是什么查询应该那么做将是从表foo_bar这样获取所有符合条件的记录，将它们传递到周围processFooBar我的包装功能，然后将提取FooBar的结构从收到的记录，然后将它们传递给C函数该做的工作并返回值。

What this query should then do would be to fetch all the the matching records from the table foo_bar, pass them to my wrapper function around processFooBar, which will then extract FooBar structs from the records received and then pass them to the C function that does the work and returns the value.

它的简单使用（伪）code解释：

Its simpler to explain using (pseudo)code:

#ifdefined __cplusplus
extern "C" {
#endif

  /* this is the wrapper function that mySQL calls and passes the records to */
  double my_wrapper_func(/*Matching rows sent by mySQL + other info .. ?*/)
  {
     /* create FooBar Array from received record */
     struct FooBar ** the_array = ExtractArrayFromRowset(/*some params*/);
     double result = processFooBar(the_array, ARRAY_SIZE_MACRO(*the_array));

     /* free resources */
     FreeFooBarArray(the_array);
     RETURN_DOUBLE(result);  /* or similar macro to return a double in MySQL */
  }

#ifdefined __cplusplus
};
#endif

任何人都可以提供一个小片段（或直接我一个片断），显示我怎么可以写my_wrapper_func - 更重要的一点还是如上所述，作为我如何实现写集合函数所需的功能在C / C ++的扩展功能。

Could anyone provide a little snippet (or direct me to a snippet) that shows me how I can write the my_wrapper_func - or more to the point how I can implement the required functionality of writing an aggregate function as described above, as an extension function in C/C++.

推荐答案

不回答你的问题，但在MySQL UDF文章是pretty好：

Doesn't answer your question but article on MySQL udf is pretty good:

HTTP：//www.$c$cproject.com/ KB /数据库/ MySQL的％5FUDFs.aspx

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