The basic idea here is to find all of the gaps first to determine how much you need to decrement each id. Then, you have to iterate through both tables and apply the decrement. (You'll need to add: host, db, user, pass, and the actual table names)
try {
$pdo = new PDO('mysql:host=HOST;dbname=DB', 'user', 'pass');
$pdo->beginTransaction();
// Iterate through all id's in the first table
$stmt = $pdo->exec('SELECT image_id FROM TableOne ORDER BY image_id ASC');
$stmt->bindColumn('image_id', $id);
if(!$stmt->fetch(PDO::FETCH_BOUND)) {
throw Exception('No rows in table');
}
$lastId = $id;
$gaps = array();
// Find all the gaps
while($stmt->fetch(PDO::FETCH_BOUND)) {
if($id != ($lastId + 1)) {
$gaps[] = $id;
}
$lastId = $id;
}
if(!isset($gaps[0])) {
throw new Exception('No gaps found');
}
// For each gap, update the range from the last gap to that gap by subtracting
// the number of gaps there has been from the id
$lastGap = $gaps[0];
for($i = 1; $i < count($gaps); $i++) {
$stmt = $pdo->prepare('UPDATE TableOne SET image_id = image_id - :i WHERE image_id BETWEEN :lastGap AND :gap');
$stmt->execute(array(
':i' => $i,
':lastGap' => $lastGap,
':gap' => $gaps[$i]
));
$stmt = $pdo->prepare('UPDATE TableTwo SET image_id = image_id - :i WHERE image_id BETWEEN :lastGap AND :gap');
$stmt->execute(array(
':i' => $i,
':lastGap' => $lastGap,
':gap' => $gaps[$i]
));
$lastGap = $gaps[$i];
}
// Finally, fix the gap between the last found gap and the end of the table
$stmt = $pdo->prepare('UPDATE TableOne SET image_id = image_id - :i WHERE image_id BETWEEN :lastGap AND :gap');
$stmt->execute(array(
':i' => $i,
':lastGap' => $lastGap,
':gap' => $gaps[$i]
));
$stmt = $pdo->prepare('UPDATE TableTwo SET image_id = image_id - :i WHERE image_id BETWEEN :lastGap AND :lastId');
$stmt->execute(array(
':i' => $i,
':lastGap' => $lastGap,
':lastId' => $lastId
));
// Verify everything is correct
$stmt = $pdo->exec('SELECT image_id FROM TableOne ORDER BY image_id ASC');
$stmt->bindColumn('image_id', $id);
if(!$stmt->fetch(PDO::FETCH_BOUND)) {
throw new Exception('No rows'); // Should never be thrown
}
$lastId = $id;
while($stmt->fetch(PDO::FETCH_BOUND)) {
if($id != ($lastId + 1)) {
throw new Exception('There was an error between ids ' . $lastId . ' and '. $id);
}
$lastId = $id;
}
$stmt = $pdo->exec('SELECT image_id FROM TableTwo ORDER BY image_id ASC');
$stmt->bindColumn('image_id', $id);
if(!$stmt->fetch(PDO::FETCH_BOUND)) {
throw new Exception('No rows in table two'); // Shouldn't hit this
}
$lastId = $id;
$ids = array($id);
while($stmt->fetch(PDO::FETCH_BOUND)) {
$ids[] = $id;
if(count($ids) == 2) {
if($ids[0] !== $ids[1]) {
throw new Exception('Table two error on ids ');
}
if($ids[0] !== $lastId) {
throw new Exception('Table two error on id gapfix');
}
$lastId = $ids[0];
$ids = array();
}
}
$pdo->commit();
} catch(Exception $e) {
$pdo->rollBack();
var_dump($e);
}
Important: You might want to throw this in a file and run via the CLI: php -f gapfix.php and include a query before $pdo->commit() that returns a list of all the ids so you can verify the operation worked as expected. If it didn't, you can roll it back as if nothing happened. The code now checks for itself if the first table is in the right order. It doesn't however check the second table yet. All checking has been implemented!