update next row based on previous ID - mysql

Question

let say i have a table named banners. the columns are:
+---+-------------------------------+
|ID | link | image | active |
+---+-------+-------------+---------+
|1 |#link1 | image1 | 0 |
|2 |#link2 | image2 | 1 |
|3 |#link3 | image3 | 0 |
+---+-------+-------------+---------+
there you can see row #2 is active. how can i update next row based on latest active row? also if active row is the last row, then set first row as active row.
PS: I will do the query using cron, update every 2 hours for example. no problem about the cron, I did it.

Answer 1

use this stored procedure :
DELIMITER //
CREATE PROCEDURE updateActiveRow()
BEGIN
SELECT MAX(ID) INTO #activeID FROM banners WHERE active;
UPDATE banners SET active=1 WHERE ID > #activeID LIMIT 1;
IF ROW_COUNT() = 0 THEN
UPDATE banners SET active=1 ORDER BY ID LIMIT 1;
END IF;
UPDATE banners SET active=0 WHERE ID = #activeID;/*do this only if you want to deactivate current active row*/
END //

Answer 2

Thanks to all,
I solved it myself. here is the code
class Job{
private $con;
function __construct(){
$this->con = mysqli_connect('localhost', 'root', '', 'egoji');
}
function getCurrentActiveID(){
$q = "SELECT id FROM banners WHERE active='1'";
$result = $this->con->query($q);
$row = mysqli_fetch_assoc($result);
return $row['id'];
}
function getNextID($id){
$q = "SELECT MIN(id) AS id FROM banners WHERE id > '{$id}'";
$result = $this->con->query($q);
$row = mysqli_fetch_assoc($result);
return $row['id'];
}
function isLastRow(){
$currentActiveId = $this->getCurrentActiveID();
$q = "SELECT id FROM banners ORDER BY id DESC LIMIT 1";
$result = $this->con->query($q);
$row = mysqli_fetch_assoc($result);
return $row['id'] == $currentActiveId ? true:false;
}
function updateFirstRow(){
$q = "SELECT MIN(id) AS id FROM banners";
$result = $this->con->query($q);
$row = mysqli_fetch_assoc($result);
$this->deactivateAll();
$update_q = "UPDATE banners SET active='1' WHERE id='{$row['id']}'";
$this->con->query($update_q);
}
function updateNextRow(){
$currentActiveId = $this->getCurrentActiveID();
$nextID = $this->getNextID($currentActiveId);
$this->deactivateAll();
$update_q = "UPDATE banners SET active='1' WHERE id='{$nextID}'";
$this->con->query($update_q);
}
function deactivateAll(){
$update_q = "UPDATE banners SET active='0'";
$this->con->query($update_q);
}
function doit(){
if($this->isLastRow()){
$this->updateFirstRow();
}else{
$this->updateNextRow();
}
}
}
$job = new Job;
$job->doit();
I am open to any suggestions or correction.

Answer 3

Tested SQL Fiddle
SET #activeID = (SELECT ID FROM Banners WHERE active = 1);
SET #isLast = (SELECT COUNT(*) FROM Banners) LIKE #activeID;
UPDATE Banners
SET active = IF(ID = #activeID, 0, IF(ID = #activeID+1, 1, active));
UPDATE Banners
SET active = IF(#isLast AND ID = 1, 1, active);