Check for mysql ID skips php

say in mysql I have a column that's id, just int auto increment.

Is there any way I can use php to tell me when there is an id that's been removed?

Like say i have

5 6 7 8 10

I need it to tell me that the 9 is missing, and continue this for all the id's. Is the开发者_高级运维re any way to do this?

Thanks

---

You need a table that contains all values. Then it's simple to do a left join to find missing ids.

create table all_values
(id int not null) engine = myisam;

insert into all_values (id) values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);

create table existing_values like all_values;

insert into existing_values (id) values (5),(6),(7),(8),(10);

select a.id from all_values as a
left join existing_values as b
on a.id = b.id
where b.id is null

---

Here is one way to do it:
1. Select all IDs from the table.
2. Assing them all to a %hash:
5 => 1
6 => 1
7 => 1
8 => 1
10 = > 1

So your ID is a key of the hash and the value is 1.

1. Create a for loop
   

for (my $i = 1; $i < 11; $i++)
{
   if($hash{$i} != 1)
   {
      print "ID $i is missing \n";
   }
}

This is Perl syntax, but PHP should be pretty similar.

---

If you can live with not getting a gap before the first id in the database (and a query using 'temporary table', 'filesort' and 'join buffer'):

SELECT
    a.id + 1 AS `From`,
    MIN(b.id - 1) AS `To`
FROM
    foo as a, foo as b
WHERE
    a.id < b.id
GROUP BY
    a.id
HAVING
    a.id < min(b.id) -1

---

self-contained example:

<?php
$pdo = new PDO('mysql:host=localhost;dbname=test;charset=utf8', 'localonly', 'localonly');
$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

// usually I create temporary tables for example scripts, but
// self-joins don't work on temp tables in mysql, bare me....
$pdo->exec('CREATE TABLE soFoo ( id int, primary key(id))');
$pdo->exec('INSERT INTO soFoo (id) VALUES (5),(6),(7),(8),(10),(15),(21)');

foreach( $pdo->query('
    SELECT
        a.id + 1 AS `From`,
        MIN(b.id - 1) AS `To`
    FROM
        foo as a, foo as b
    WHERE
        a.id < b.id
    GROUP BY
        a.id
    HAVING
        a.id < min(b.id) -1', PDO::FETCH_ASSOC) as $row
) {
    echo $row['From'], ' - ', $row['To'], "\n";
}

prints

9 - 9
11 - 14
16 - 20