WHILE Loop with insert not working as expected - mysql

Question

I am try to find all child and sub-child of a given parent, but not getting desired output if I use WHILE loop. Surprisingly, if I execute the scripts manually, it works as expected. Please have a look at below script.
DROP TABLE IF EXISTS test;
CREATE TABLE test (id INT, parent_id INT);
INSERT INTO test VALUES (1,NULL);
INSERT INTO test VALUES (2,1);
INSERT INTO test VALUES (3,2);
INSERT INTO test VALUES (4,2);
INSERT INTO test VALUES (5,3);
INSERT INTO test VALUES (6,4);
INSERT INTO test VALUES (7,2);
INSERT INTO test VALUES (8,4);
INSERT INTO test VALUES (9,1);
INSERT INTO test VALUES (10,1);
COMMIT;
DELIMITER $$
USE `test`$$
DROP PROCEDURE IF EXISTS `get_parent_child_hierarchy`$$
CREATE PROCEDURE `get_parent_child_hierarchy`(Parent_ID INT)
BEGIN
DECLARE `rowcount` INT DEFAULT 1;
DROP TABLE IF EXISTS Temp;
CREATE TABLE Temp(ParentID INT, ChildID INT, Stage INT);
INSERT INTO Temp(ParentID, ChildID, Stage)
SELECT Parent_ID, Parent_ID, 2;
WHILE rowcount > 0 DO
UPDATE Temp
SET Stage = 1
WHERE Stage = 2;
COMMIT;
INSERT INTO Temp(ParentID, ChildID, Stage)
SELECT Parent_ID, id, 2
FROM Test T
WHERE Parent_id IN (SELECT ChildID
FROM Temp
WHERE Stage = 1
AND Temp.ChildID <> T.id);
UPDATE Temp
SET Stage = 0
WHERE Stage = 1;
COMMIT;
SET rowcount = (SELECT COUNT(ChildID)
FROM Temp
WHERE Stage = 2);
END WHILE;
SELECT *
FROM Temp
WHERE Parent_ID <> ChildID;
DROP TABLE IF EXISTS Temp;
END$$
DELIMITER ;
Input: 2
Expected Output:
ParentID | ChildID | Stage
---------|---------|------
2 | 3 | 0
2 | 4 | 0
2 | 5 | 0
2 | 6 | 0
2 | 7 | 0
2 | 8 | 0
But unfortunately, when the run the script using WHILE loop, I get all the rows in the input.
Any help is appreciated.
I agree this is moreover specific problem than issue with technical stuff. But I wonder if there is any issue with MySQL, when you use WHILE loop and INSERT.

Answer 1

You defined input parameter's name as Parent_ID which is a column in table test, this is reason that you did not get what you expected.
Try following;)
CREATE PROCEDURE `get_parent_child_hierarchy`(pid INT)
BEGIN
DECLARE `rowcount` INT DEFAULT 1;
DROP TABLE IF EXISTS Temp;
CREATE TABLE Temp(ParentID INT, ChildID INT, Stage INT);
INSERT INTO Temp(ParentID, ChildID, Stage)
SELECT pid, pid, 2;
WHILE rowcount > 0 DO
UPDATE Temp
SET Stage = 1
WHERE Stage = 2;
COMMIT;
INSERT INTO Temp(ParentID, ChildID, Stage)
SELECT pid, id, 2
FROM test T
WHERE parent_id IN (SELECT ChildID
FROM Temp
WHERE Stage = 1
AND Temp.ChildID <> T.id);
UPDATE Temp
SET Stage = 0
WHERE Stage = 1;
COMMIT;
SET rowcount = (SELECT COUNT(ChildID)
FROM Temp
WHERE Stage = 2);
END WHILE;
SELECT *
FROM Temp
WHERE pid <> ChildID;
DROP TABLE IF EXISTS Temp;
END