对一个MySQL存储过程的优化

在编写MySQL存储过程的过程中，我们会时不时地需要对某些存储过程进行优化，其目的是确保代码的可读性、正确性及运行性能。本文以作者实际工作为背景，介绍了对某一个MySQL存储过程优化的整个过程。

在本文中，需要被优化的存储过程如下：

drop procedure if exists pr_dealtestnum;
delimiter //

create procedure pr_dealtestnum
(
   in    p_boxnumber    varchar(30)
)
pr_dealtestnum_label:begin

       insert into tb_testnum select boxnumber,usertype from tb_testnum_tmp where boxnumber= p_boxnumber;

       leave pr_dealtestnum_label;
end;
//
delimiter ;
select 'create procedure pr_dealtestnumok';

在存储过程中使用到的表tb_testnum结构如下：

drop table if exists tb_testnum;

create table tb_testnum
(
   boxnumber  varchar(30)  not null,
   usertype   int          not null                                                                                 
);
create unique index idx1_tb_testnum ontb_testnum(boxnumber);

在存储过程中使用到的另外一张表tb_testnum_tmp结构如下：

drop table if exists tb_testnum_tmp;

create table tb_testnum_tmp
(
   boxnumber  varchar(30)  not null,
   usertype   int          not null    
);
create unique index idx1_tb_testnum_tmp ontb_testnum_tmp(boxnumber);

从两个表的结构可以看出，tb_testnum和tb_testnum_tmp所包含的字段完全相同，存储过程pr_dealtestnum的作用是根据输入参数将tb_testnum_tmp表的数据插入到tb_testnum表中。

很明显，虽然能够实现预期的功能，但存储过程pr_dealtestnum的代码还有改进的地方。下面，我们一步一步来对其进行优化。

优化一
存储过程pr_dealtestnum的主体是一条insert语句，但这条insert语句里面又包含了select语句，这样的编写是不规范的。因此，我们要把这条insert语句拆分成两条语句，即先把数据从tb_testnum_tmp表中查找出来，再插入到tb_testnum表中。修改之后的存储过程如下：

drop procedure if exists pr_dealtestnum;
delimiter //

create procedure pr_dealtestnum
(
   in    p_boxnumber    varchar(30)
)
pr_dealtestnum_label:begin
       declare  p_usertype    int;

       select usertype into p_usertype from tb_testnum_tmp where boxnumber=p_boxnumber;

       insert into tb_testnum values(p_boxnumber,p_usertype);

       leave pr_dealtestnum_label;
end;
//
delimiter ;
select 'create procedure pr_dealtestnum ok';

优化二
在向tb_testnum表插入数据之前，要判断该条数据在表中是否已经存在了，如果存在，则不再插入数据。同理，在从tb_testnum_tmp表中查询数据之前，要先判断该条数据在表中是否存在，如果存在，才能从表中查找数据。修改之后的存储过程如下：

drop procedure if exists pr_dealtestnum;
delimiter //

create procedure pr_dealtestnum
(
   in    p_boxnumber    varchar(30)
)
pr_dealtestnum_label:begin
       declare  p_usertype   int;
       declare  p_datacount  int;

       select count(*) into p_datacount from tb_testnum_tmp where boxnumber=p_boxnumber;
       if p_datacount > 0 then
       begin
           select usertype into p_usertype fromtb_testnum_tmp where boxnumber=p_boxnumber;
       end;
       else
       begin
           leave pr_dealtestnum_label;
       end;
       end if;

       select count(*) into p_datacount from tb_testnum where boxnumber=p_boxnumber;
       if p_datacount = 0 then
       begin
           insert into tb_testnum values(p_boxnumber,p_usertype);
           leave pr_dealtestnum_label;
       end;
       else
       begin
           leave pr_dealtestnum_label;
       end;
       end if;
end;
//
delimiter ;
select 'create procedure pr_dealtestnum ok';

优化三
不管向tb_testnum表插入数据的操作执行成功与否，都应该有一个标识值来表示执行的结果，这样也方便开发人员对程序流程的追踪和调试。也就是说，在每条leave语句之前，都应该有一个返回值，我们为此定义一个输出参数。修改之后的存储过程如下：

drop procedure if exists pr_dealtestnum;
delimiter //

create procedure pr_dealtestnum
(
   in    p_boxnumber  varchar(30),
   out   p_result     int  -- 0-succ, other-fail
)
pr_dealtestnum_label:begin
       declare  p_usertype   int;
       declare  p_datacount  int;

       select count(*) into p_datacount from tb_testnum_tmp where boxnumber=p_boxnumber;
       if p_datacount > 0 then
       begin
           select usertype into p_usertype from tb_testnum_tmp where boxnumber=p_boxnumber;
       end;
       else
       begin
           set p_result = 1;
           leave pr_dealtestnum_label;
       end;
       end if;

       select count(*) into p_datacount from tb_testnum where boxnumber=p_boxnumber;
       if p_datacount = 0 then
       begin
           insert into tb_testnum values(p_boxnumber,p_usertype);
           set p_result = 0;
           leave pr_dealtestnum_label;
       end;
       else
       begin
           set p_result = 2;
           leave pr_dealtestnum_label;
       end;
       end if;
end;
//
delimiter ;
select 'create procedure pr_dealtestnum ok';

优化四
我们注意到“insert into tb_testnum values(p_boxnumber,p_usertype);”语句中，tb_testnum表之后没有列出具体的字段名，这个也是不规范的。如果在以后的软件版本中，tb_testnum表中新增了字段，那么这条insert语句极有可能会报错。因此，规范的写法是无论tb_testnum表中有多少字段，在执行insert操作时，都要列出具体的字段名。修改之后的存储过程如下：

drop procedure if exists pr_dealtestnum;
delimiter //

create procedure pr_dealtestnum
(
   in    p_boxnumber  varchar(30),
   out   p_result     int   -- 0-succ, other-fail
)
pr_dealtestnum_label:begin
       declare  p_usertype   int;
       declare  p_datacount  int;

       select count(*) into p_datacount from tb_testnum_tmp where boxnumber=p_boxnumber;
       if p_datacount > 0 then
       begin
           select usertype into p_usertype from tb_testnum_tmp where boxnumber=p_boxnumber;
       end;
       else
       begin
           set p_result = 1;
           leave pr_dealtestnum_label;
       end;
       end if;

       select count(*) into p_datacount from tb_testnum where boxnumber=p_boxnumber;
       if p_datacount = 0 then
       begin
           insert into tb_testnum(boxnumber,usertype) values(p_boxnumber,p_usertype);
           set p_result = 0;
           leave pr_dealtestnum_label;
       end;
       else
       begin
           set p_result = 2;
           leave pr_dealtestnum_label;
       end;
       end if;
end;
//
delimiter ;
select 'create procedure pr_dealtestnum ok';

优化五
在执行insert语句之后，要用MySQL中自带的@error_count参数来判断插入数据是否成功，方便开发人员跟踪执行结果。如果该参数的值不为0，表示插入失败，那么我们就用一个返回参数值来表示操作失败。修改之后的存储过程如下：

drop procedure if exists pr_dealtestnum;
delimiter //

create procedure pr_dealtestnum
(
    in    p_boxnumber varchar(30),
    out   p_result    int   -- 0-succ, other-fail
)
pr_dealtestnum_label:begin
       declare  p_usertype   int;
       declare  p_datacount  int;

       select count(*) into p_datacount from tb_testnum_tmp where boxnumber=p_boxnumber;
       if p_datacount> 0 then
       begin
           select usertype into p_usertype from tb_testnum_tmp where boxnumber=p_boxnumber;
       end;
       else
       begin
           set p_result = 1;
           leave pr_dealtestnum_label;
       end;
       end if;

       select count(*) into p_datacount from tb_testnum where boxnumber=p_boxnumber;
       if p_datacount = 0then
       begin
           insert into tb_testnum(boxnumber,usertype) values(p_boxnumber,p_usertype);
           if @error_count<>0 then
           begin
               set p_result= 3;
           end;
           else
           begin
               set p_result= 0;
           end;
           end if;
       end;
       else
       begin
           set p_result = 2;
       end;
       end if;

       leave pr_dealtestnum_label;
end;
//
delimiter ;
select 'create procedure pr_dealtestnum ok';

结束语
从上面可以看出，一个短短的存储过程，就有这么多需要优化的地方，看来存储过程的编写也不是一件很简单的事情。确实，我们在编写代码(不仅仅是存储过程)的时候，一定要从代码的功能、可读性、性能等多方面来考虑，这样才能够写出优美的、具备较长生命周期的代码，进而开发出高质量的软件产品。