For loop example in MySQL - mysql

Question

In MySQL, I have this stored procedure with a LOOP:
DELIMITER $$
CREATE PROCEDURE ABC()
BEGIN
DECLARE a INT Default 0 ;
simple_loop: LOOP
SET a=a+1;
select a;
IF a=5 THEN
LEAVE simple_loop;
END IF;
END LOOP simple_loop;
END $$
It always prints 1. What is the correct syntax for a MySQL Loop?

Answer 1

drop table if exists foo;
create table foo
(
id int unsigned not null auto_increment primary key,
val smallint unsigned not null default 0
)
engine=innodb;
drop procedure if exists load_foo_test_data;
delimiter #
create procedure load_foo_test_data()
begin
declare v_max int unsigned default 1000;
declare v_counter int unsigned default 0;
truncate table foo;
start transaction;
while v_counter < v_max do
insert into foo (val) values ( floor(0 + (rand() * 65535)) );
set v_counter=v_counter+1;
end while;
commit;
end #
delimiter ;
call load_foo_test_data();
select * from foo order by id;

Answer 2

While loop syntax example in MySQL:
delimiter //
CREATE procedure yourdatabase.while_example()
wholeblock:BEGIN
declare str VARCHAR(255) default '';
declare x INT default 0;
SET x = 1;
WHILE x <= 5 DO
SET str = CONCAT(str,x,',');
SET x = x + 1;
END WHILE;
select str;
END//
Which prints:
mysql> call while_example();
+------------+
| str |
+------------+
| 1,2,3,4,5, |
+------------+
REPEAT loop syntax example in MySQL:
delimiter //
CREATE procedure yourdb.repeat_loop_example()
wholeblock:BEGIN
DECLARE x INT;
DECLARE str VARCHAR(255);
SET x = 5;
SET str = '';
REPEAT
SET str = CONCAT(str,x,',');
SET x = x - 1;
UNTIL x <= 0
END REPEAT;
SELECT str;
END//
Which prints:
mysql> call repeat_loop_example();
+------------+
| str |
+------------+
| 5,4,3,2,1, |
+------------+
FOR loop syntax example in MySQL:
delimiter //
CREATE procedure yourdatabase.for_loop_example()
wholeblock:BEGIN
DECLARE x INT;
DECLARE str VARCHAR(255);
SET x = -5;
SET str = '';
loop_label: LOOP
IF x > 0 THEN
LEAVE loop_label;
END IF;
SET str = CONCAT(str,x,',');
SET x = x + 1;
ITERATE loop_label;
END LOOP;
SELECT str;
END//
Which prints:
mysql> call for_loop_example();
+-------------------+
| str |
+-------------------+
| -5,-4,-3,-2,-1,0, |
+-------------------+
1 row in set (0.00 sec)
Do the tutorial: http://www.mysqltutorial.org/stored-procedures-loop.aspx
If I catch you pushing this kind of MySQL for-loop constructs into production, I'm going to shoot you with the foam missile launcher. You can use a pipe wrench to bang in a nail, but doing so makes you look silly.

Answer 3

Assume you have one table with name 'table1'. It contain one column 'col1' with varchar type. Query to crate table is give below
CREATE TABLE `table1` (
`col1` VARCHAR(50) NULL DEFAULT NULL
)
Now if you want to insert number from 1 to 50 in that table then use following stored procedure
DELIMITER $$
CREATE PROCEDURE ABC()
BEGIN
DECLARE a INT Default 1 ;
simple_loop: LOOP
insert into table1 values(a);
SET a=a+1;
IF a=51 THEN
LEAVE simple_loop;
END IF;
END LOOP simple_loop;
END $$
To call that stored procedure use
CALL `ABC`()

Answer 4

You can exchange this local variable for a global, it would be easier.
DROP PROCEDURE IF EXISTS ABC;
DELIMITER $$
CREATE PROCEDURE ABC()
BEGIN
SET #a = 0;
simple_loop: LOOP
SET #a=#a+1;
select #a;
IF #a=5 THEN
LEAVE simple_loop;
END IF;
END LOOP simple_loop;
END $$