Question

我有两张桌子（这里简化了很多）：

QUADRI

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// config

weather.config(function($routeProvider) {
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})
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</html>

勒

ID SBR_750 b10C  TGI
---------------------
Q1    0      1    0
Q2    2      1    0
Q3    1      0    1

我希望这个结果在CELLE：

CELLANAME NEEDED READY
----------------------
SBR_750    NULL   12
b10C       NULL   10
TGI        NULL    5

我尝试编写存储过程但它不起作用：ERROR 1210.EXECUTE的参数不正确。

以下是代码：

CELLANAME NEEDED READY
------------------------
SBR_750     3     12
b10C        2     10
TGI         1      5

更新：它不起作用所以我改变策略：

CREATE DEFINER=`root`@`%.zamberlan.local` PROCEDURE `AggiornaCelle`(IN nomecella varchar(15))
BEGIN
set @s='update celle set needed=(select sum(?) from quadri) where cellaname=?';
set @NC=nomecella;
prepare stmt from @s;
execute stmt using @NC;
deallocate prepare stmt;
END

受mysql, iterate through column names启发。

但是我收到错误“光标未打开...”

Answer 1

您确实需要使用动态SQL来执行此操作。 Celle从quadri知道它需要的所有列，因此你可以从这个事实推动动态语句的创建。使用游标是一种很好的方式。

drop table if exists quadri;
create table quadri(ID varchar(2),SBR_750 int, b10C int, TGI int);
insert into quadri values
('Q1' ,   0 ,     1 ,   0),
('Q2' ,   2 ,     1 ,   0),
('Q3' ,   1 ,     0 ,   1);

drop table if exists celle;
create table CELLE (CELLANAME varchar(20) ,NEEDED int,READY int);
insert into celle values
('SBR_750'  ,  NULL ,  12),
('b10C'     ,  NULL ,  10),
('TGI'      ,  NULL ,   5);

drop procedure if exists `AggiornaCelle`;
delimiter $$

CREATE DEFINER=`root`@`localhost` PROCEDURE `AggiornaCelle`()
begin
DECLARE done INT DEFAULT FALSE;
declare col_name varchar(20);
declare cur1 CURSOR FOR 
 SELECT cellaname FROM celle ;

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

open cur1;
read_loop: loop
        fetch cur1 into col_name;
        if done then leave read_loop; end if;
        set @sqlstr = concat('update celle set needed = (select sum(',col_name,') from quadri) where cellaname = ', char(39),col_name,char(39),';'); 
        insert into debug_table (msg) values(@sqlstr);
        prepare stmt from @sqlstr;
        execute stmt ;
        deallocate prepare stmt;
end loop;
close cur1;
end $$
delimiter ;

truncate table debug_table;
call `AggiornaCelle`();
select * from debug_table;
select * from celle;

MariaDB [sandbox]> select * from debug_table;
+----+------------------------------------------------------------------------------------------+------+
| id | msg                                                                                      | MSG2 |
+----+------------------------------------------------------------------------------------------+------+
|  1 | update celle set needed = (select sum(SBR_750) from quadri) where cellaname = 'SBR_750'; | NULL |
|  2 | update celle set needed = (select sum(b10C) from quadri) where cellaname = 'b10C';       | NULL |
|  3 | update celle set needed = (select sum(TGI) from quadri) where cellaname = 'TGI';         | NULL |
+----+------------------------------------------------------------------------------------------+------+
3 rows in set (0.00 sec)

MariaDB [sandbox]> select * from celle;
+-----------+--------+-------+
| CELLANAME | NEEDED | READY |
+-----------+--------+-------+
| SBR_750   |      3 |    12 |
| b10C      |      2 |    10 |
| TGI       |      1 |     5 |
+-----------+--------+-------+
3 rows in set (0.00 sec)

debug_table只存在，以便我可以检查更新语句。

Answer 2

根据 documentation

设置@ s ='更新celle set needed =（从quadri中选择sum（？））其中cellaname =？';

你应该通过两个论点。

execute stmt using @NC;

应该是类似的东西

execute stmt using @NC, @NC;

@NC与尝试更新celle中的行相同，与quadri表中的列名相同。

如何使用execute语句更新表？

2 个答案: