I started on stored procedures with MySQL PHPMyAdmin 5.5 3.4 after watching the tutorial found on this site I took this example (the tutorial siteduzero)
I reproduced the same result without
The problem is that the process is slow in execution, it continues loading without displaying results after 2 min I close the page, creating the procedure is done correctly. Here's the code:
CREATE DEFINER=`root`#`localhost` PROCEDURE `AfficherMarques`(OUT `Marques` VARCHAR(25))
BEGIN
DECLARE done INT DEFAULT 0;
DECLARE Marques VARCHAR(25);
DECLARE pointeur CURSOR FOR SELECT DISTINCT marque FROM marchands GROUP BY marque;
DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1;
OPEN pointeur;
REPEAT
FETCH pointeur INTO Marques;
IF done = 0 THEN
SELECT Marques;
END IF;
UNTIL done END REPEAT;
CLOSE pointeur;
END
Related
I must find the sum of the first 100 natural numbers. 1+2+3+...+n, and so on. While using "while loops".
delimiter $
create procedure `calcul`.somme()
begin
declare s int default 0;
declare i int default 1;
while(i<=100) do
set s := s+i;
set i := i+1;
end while;
select s;
end;
$
call `calcul`.somme()
when I call the somme() I'm getting this error -->
call calcul.somme()= Error Code: 2013. Lost connection to MySQL server during query
The query is taking too long and the engine is timing out.
You can edit the SQL Editor preferences in MySQL Workbench:
In the application menu, select Edit > Preferences > SQL Editor.
Look for the MySQL Session section and increase the DBMS connection read time out value.
Save the settings, quite MySQL Workbench and reopen the connection.
use calcul;
delimiter $
create procedure somme()
begin
declare s int default(0);
declare i int default(1);
while(i<=100) do
set s := s+i;
set i := i+1;
end while;
select s;
end;
$
CALL somme()
thanks, the Problem solved 👌
I usually work with Oracle database and when creating stored procedures one can write cursors where the where clause can have a variable, value of which can be provided at run time.
How do you write something similar in mySQL
Something like
DECLARE myCursor cursor select col1 from table1 where col2 = &1;
OPEN myCursor ("NEW");
You may use user-defined variable and/or local variable (including procedure parameters), both assigned externally and calculated internally, in the cursor definition:
CREATE PROCEDURE test_proc( {parameters} )
BEGIN
DECLARE _id_ INT;
DECLARE cur CURSOR FOR
SELECT id FROM test WHERE val = {variable};
DECLARE EXIT HANDLER FOR NOT FOUND
BEGIN
CLOSE cur;
END;
OPEN cur;
LOOP
FETCH cur INTO _id_;
SELECT _id_;
END LOOP;
END
But you cannot to alter the parameter "on the fly" - after cursor is opened the changes in its parameters will be iglored (during the opening the cursor's text is fixed, the values instead of names are used in fixed text).
Hence when you need to alter dynamically assigned parameter then you must close and reopen the cursor.
DEMO fiddle
I get this error in the following stored procedure Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1; OPEN cur1; count' at line 13
DELIMITER $$
DROP PROCEDURE IF EXISTS cursor_example
$$
CREATE PROCEDURE cursor_example()
READS SQL DATA
BEGIN
DECLARE i_Name CHAR(3);
DECLARE i_SurfaceArea FLOAT(10,2);
DECLARE done INT DEFAULT 0;
DECLARE cur1 CURSOR FOR
SELECT Name, SurfaceArea
FROM country
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;
OPEN cur1;
country_loop:LOOP
FETCH cur1 INTO i_Name, i_SurfaceArea;
IF done=1 THEN
LEAVE country_loop;
END IF;
END LOOP country_loop;
CLOSE cur1;
END;
$$
DELIMITER ;
Just generally how the whole procedure is suppose to work and what is it for.
Thanks.
You were missing a semi-colon after FROM country. Use the following pattern:
DROP PROCEDURE IF EXISTS cursor_example;
DELIMITER $$
CREATE PROCEDURE cursor_example()
READS SQL DATA
BEGIN
DECLARE i_Name CHAR(3);
DECLARE i_SurfaceArea FLOAT(10,2);
DECLARE done INT DEFAULT 0;
DECLARE cur1 CURSOR FOR
SELECT Name, SurfaceArea
FROM country;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;
OPEN cur1;
country_loop:LOOP
FETCH cur1 INTO i_Name, i_SurfaceArea;
IF done=1 THEN
LEAVE country_loop;
END IF;
-- right here is where you do stuff with those variables
END LOOP country_loop;
CLOSE cur1;
END;
$$
DELIMITER ;
I don't understand with the example is trying to FETCH cur1 INTO in
the example is for?
Remember that the CURSOR is just a select stmt. It can be really complicated with joins, you name it. But in the end it has a select column list. In your case it has 2 columns coming back. So the FETCH, one row at a time, brings the current row into LOCAL VARIABLES (in the respective order from the cursor list to the variables you list). You declared those LOCAL VARIABLES in your DECLAREs.
When you are out of rows, the HANDLER sets done to 1 and you bail out of the loop.
As for the DELIMITER read the last half of this answer of mine Here.
Just generally how the whole procedure is suppose to work and what is
it for?
Described above mostly. Cursors are for procedural handling of data returned. Allowing you to inject procedural thinking into solving problems. By the way they are terribly slow and should be avoided whenever possible. They are typically a crutch for devs new to SQL that can't get their head into how to do work with sets and relations. That is, the way high performance RDBMS's excel at.
That said, experienced SQL devs are known to use them for tricky situations.
I have a mysql stored procedure made it recursively, it always returned 499 rows max.
my stored procedure is moving in a tree (not a binary tree) and check the nodes if they have children and so on until it reached the leaves.
I don't know how can I convert my code into non-recursive way, I just want to ask for tow points:
how can I make an infinite recursive in mysql(mysql server version is 5.5)?
if that can't happened, how can I change my cod into non-recursive way?
CREATE PROCEDURE `get_citations`(in _pub_id int(10),in _lvl int,citation_count int)
BEGIN
DECLARE done INT DEFAULT FALSE;
declare p_id,c_count int;
declare _counter int default 1;
DECLARE cur1 CURSOR FOR SELECT pat_publn_id,cited_count from temp.a_citations
where pub_parent=_pub_id ;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
insert into a_citations
(pat_publn_id ,
publn_nr ,
publn_kind,
publn_auth,
publn_date,
cited_pat_publn_id,
cited_count,
pub_lvl,
pub_parent)
(select p.pat_publn_id,p.publn_nr,p.publn_kind,p.publn_auth,p.publn_date,c.cited_pat_publn_id,
(select count(*) as cnt FROM patstat1304.tls212_citation c2 where c2.cited_pat_publn_id=c.pat_publn_id) as cited_count,_lvl as pub_lvl,_pub_id as pub_parent
from patstat1304.tls212_citation c,patstat1304.tls211_pat_publn p
where c.pat_publn_id=p.pat_publn_id and c.cited_pat_publn_id=_pub_id);
commit;
OPEN cur1;
read_loop: LOOP
fetch cur1 into p_id,c_count;
IF (c_count !=0) then
call get_citations( p_id,_lvl+1,c_count);
commit;
END if;
IF done THEN
LEAVE read_loop;
END IF;
set _counter=_counter+1;
if(_counter=citation_count) then
LEAVE read_loop;
end if;
end loop;
CLOSE cur1;
END
MySQL can not execute stored procedures with a very deep nesting.
Very soon, error ER_STACK_OVERRUN_NEED_MORE will appear.
Increasing the thread stack to go further will not work either.
To change the recursive call to a non recursive one, consider something like this:
1) Create a table named publications_to_process, with the publication and search level.
2) To start the search, insert the original publication in this table, with level 1.
3) In a loop, fetch one publication, examine the citations, and add the publications listed in the publications_to_process, incrementing the level.
4) As a bonus, for cases like:
Pub_1 --> Pub_2 --> Pub_3,
Pub_1 --> Pub_3
there is no need to add Pub_3 again to the search if it has been processed already.
In other words, the publications are more likely to be a directed graph that a tree.
5) Either make the table temporary, or consider adding a PROCESSLIST_ID column, so that different sessions (having a different CONNECTION_ID()) do not step on each other, when executing this search in parallel.
I have got this stored procedure:
DELIMITER //
DROP PROCEDURE IF EXISTS cursor_example//
CREATE PROCEDURE cursor_example()
BEGIN
DECLARE niche_id INT;
DECLARE niche_name VARCHAR(100);
DECLARE curl CURSOR FOR SELECT * FROM `niche`;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;
OPEN curl;
my_loop:LOOP
FETCH curl INTO niche_id,niche_name;
IF done=1 THEN
LEAVE my_loop;
END IF;
END LOOP my_loop;
CLOSE curl;
END//
DELIMITER ;
I want to output everything that the curl fetches. So I thought to put SELECT statement inside or outside the loop..but that wouldnt give me the results that I want. How do I get back all the sql results from that cursor.
And what are the advantages of using cursors compare to other a simple unbound - SELECT statement. I mean I could get the results that I wanted by simply USING a select statement without writing all that cursor code?