How to update table using execute statement? - mysql

Question

I have two tables (much simplified here):
QUADRI
ID SBR_750 b10C TGI
---------------------
Q1 0 1 0
Q2 2 1 0
Q3 1 0 1
CELLE
CELLANAME NEEDED READY
----------------------
SBR_750 NULL 12
b10C NULL 10
TGI NULL 5
I want this result in CELLE:
CELLANAME NEEDED READY
------------------------
SBR_750 3 12
b10C 2 10
TGI 1 5
I tried to write a stored procedure but it doesn't works: ERROR 1210. Incorrect arguments to EXECUTE.
Here is the code:
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
UPDATE:
It doesn't work so I change strategy:
CREATE DEFINER=`root`#`%.zamberlan.local` PROCEDURE `AggiornaCelle`()
BEGIN
declare i int;
declare num_rows int;
declare col_name varchar(20);
DECLARE col_names CURSOR FOR
SELECT column_name
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = quadri
ORDER BY ordinal_position;
select FOUND_ROWS() into num_rows;
SET i = 1;
the_loop: LOOP
IF i > num_rows THEN
CLOSE col_names;
LEAVE the_loop;
END IF;
FETCH col_names
INTO col_name;
update celle set needed=sum(col_name) where cellaname=col_name;
SET i = i + 1;
END LOOP the_loop;
END
inspired by mysql, iterate through column names.
However I receive the error "Cursor is not open..."

Answer 1

You do need to use dynamic sql to do this. Celle knows about all the columns it needs from quadri so you could drive the creation of the dynamic statements from this fact. Using a cursor is as good a way to do it as any.
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)
The debug_table only exists so that I can check the update statements.

Answer 2

As per documentation
set #s='update celle set needed=(select sum(?) from quadri) where cellaname=?';
You are supposed to pass two argument.
execute stmt using #NC;
should be or something similar
execute stmt using #NC, #NC;
#NC would be same as you are trying to update a row in celle, which is same as column name in quadri table.