mysql05---游标

drop procedure p12$ //删除存储过程


//游标cursor,一条sql对应n条资源，取出资源的接口/句柄就是cursor,  一条sql产生的n条结果不是一次性全部输出，而是返回一个地址，然后一个个的筛选。

//声明游标（declare），打开游标(open)，打开游标就去数据库查询资源了，查到了并不是把所有的结果行返回给你，而是给你一个口，然后就可以去fetch(取值)，最后close游标。

mysql> delimiter $
create procedure p13()
begin
    declare row_gid int;
    declare row_num int;
    declare row_name varchar(20);   //声明3个变量，存储fetch得到的每一行的3个列的值
    
    declare getgoods cursor //声明游标，此时的游标是一个地址，如果查询为空则getgoods就是null,
            for select gid,num,name from goods; //游标作用的语句
    open getgoods;  //打开游标
    fetch getgoods  //fetch一次就得到一行
            into row_gid,row_num,row_name;   //一一对应赋值
    
    select row_num,row_name;  //显示出来看
    close getgoods; //关闭游标
end$

mysql> call p13()$
+---------+----------+
| row_num | row_name |
+---------+----------+
|     222 | 猫       |
+---------+----------+


mysql> delimiter $
create procedure p14()
begin
    declare row_gid int;
    declare row_num int;
    declare row_name varchar(20);  
    
    declare getgoods cursor for select gid,num,name from goods;
    open getgoods;
    
    fetch getgoods into row_gid,row_num,row_name; //相同的语句每取一次，往后移动一次，
    select row_num,row_name; 
    
    fetch getgoods into row_gid,row_num,row_name; 
    select row_num,row_name; 
    
    fetch getgoods into row_gid,row_num,row_name; 
    select row_num,row_name; 
    
    fetch getgoods into row_gid,row_num,row_name; 
    select row_num,row_name;
    
    close getgoods;
end$

mysql> call p14()$
+---------+----------+
| row_num | row_name |
+---------+----------+
|     222 | 猫       |
+---------+----------+
1 row in set

+---------+----------+
| row_num | row_name |
+---------+----------+
|     333 | 马       |
+---------+----------+
1 row in set

+---------+----------+
| row_num | row_name |
+---------+----------+
|     555 | 猪       |
+---------+----------+
1 row in set



delimiter $
create procedure p16()
begin
    declare totalcunt int default 0;//总行数
    declare i int default 0;
    
    declare row_gid int;
    declare row_num int;
    declare row_name varchar(20);  
    
    declare getgoods cursor for select gid,num,name from goods;
    
    //declare要放在一起写完，再写select语句
    select count(*) into totalcunt from goods;
    
    open getgoods;
    
    repeat    //可以在repeat中对每一行做处理
        set i:=i+1;
        fetch getgoods into row_gid,row_num,row_name; 
        select row_num,row_name; 
    until i >= totalcunt end repeat;
    
    close getgoods;
end$

mysql> call p16()$
+---------+----------+
| row_num | row_name |
+---------+----------+
|     222 | 猫       |
+---------+----------+
1 row in set

+---------+----------+
| row_num | row_name |
+---------+----------+
|     333 | 马       |
+---------+----------+
1 row in set

//游标越界时标志，在mysql cursor 中可以declare continue handler来操作是否越界，declare continue handler for NOT FOUND set ....声明continue handler专门监控没有数据事件时执行语句，

delimiter $
create procedure p17()
begin
    declare row_gid int;
    declare row_num int;
    declare row_name varchar(20);  
    
    declare outrange int default 1;//越界标志，为0时就没有了
    
    declare getgoods cursor for select gid,num,name from goods; //声明游标,返回的是select的结果集的首地址，
    
    declare continue handler for NOT FOUND set outrange:=0;//声明句柄，没有数据事件发生时，执行设置outrange为0，
    
    open getgoods;
    
    repeat    //可以在repeat中对每一行做处理
        fetch getgoods into row_gid,row_num,row_name;  //取一行
        select row_num,row_name;   //输出fetch到的哪一行
    until outrange= 0 end repeat;
    
    close getgoods;
end$

mysql> call p17()$   //多取了一行，
+---------+----------+
| row_num | row_name |
+---------+----------+
|     222 | 猫       |
+---------+----------+
1 row in set


+---------+----------+
| row_num | row_name |
+---------+----------+
|     666 | uuu      |
+---------+----------+
1 row in set

+---------+----------+
| row_num | row_name |
+---------+----------+
|     666 | uuu      |
+---------+----------+
1 row in set

repeat
    fetch getgoods into row_gid,row_num,row_name; 
    select row_num,row_name; 
until outrange= 0 end repeat;
//最后一个fetch--->没数据--->outrange=0--->因为声明的是一个continue handle,继续执行后面的sql语句，select row_num,row_name; --->因此最后一行取出2次
//如果NOT FOUND事件发生后，select不再执行就好了。声明handler不是continue而是exit就好了。


declare exit handler for NOT FOUND set outrange:=0;  //就好了
//exit与continue的区别：exit触发后后面的语句不在执行。除了continue和exit还有undo handler，
//continue是触发后后面的语句继续执行
//exit是出发后后面的语句不执行
//undo 是触发后前面的语句撤销，但是mysql不支持。


//就用continue同时还不取出最后一行，游标终极版本。
delimiter $
create procedure p20()
begin
    declare row_gid int;
    declare row_num int;
    declare row_name varchar(20);  
    
    declare outrange int default 1;
    
    declare getgoods cursor for select gid,num,name from goods;
    
    declare continue handler for NOT FOUND set outrange:=0;
    
    open getgoods;
    fetch getgoods into row_gid,row_num,row_name; //先取出一行，防止第一行就是空的
        repeat
            select row_num,row_name;  //输出fetch到的那行，
            fetch getgoods into row_gid,row_num,row_name; //fetch最后一行的下一行的时候，NOT FOUND事件触发，继续执行的是until outrange= 0 不会多取出最后一行，
        until outrange= 0 
    end repeat;
    
    close getgoods;
end$


//游标终极版本。
delimiter $
create procedure p23()
begin
    declare row_gid int;
    declare row_num int;
    declare row_name varchar(20);  
    
    declare outrange int default 1;
    
    declare getgoods cursor for select gid,num,name from goods;
    
    declare continue handler for NOT FOUND set outrange:=0;
    
    open getgoods;
    fetch getgoods into row_gid,row_num,row_name; 
        while outrange=1 do     //repeat相当于do while,
            select row_num,row_name; 
            fetch getgoods into row_gid,row_num,row_name; 
        end while;
    
    close getgoods;
end$