如何通过循环从1月更改或空数据库开始更改自动增量

Question

I have tried to reset a var $potong to start from 1 again when date = '01' and database table is empty.

Here is my code :

$month = date('n');
$b=romanNumerals($month);
$years=date('Y');
echo"<div class='form-group'>";
$tanggal=date('d'); 
$s=mysql_query('SELECT * FROM preorder ORDER BY id_po DESC LIMIT 1');

while($a=mysql_fetch_array($s)){
    $nomor = $a[2];
    $potong = (int)substr($nomor,0,3);
    $potong++;
    $awal =1;
}

$kosong= mysql_num_rows($s);
if($potong == 0 || $tanggal == 01){
    echo"<input type='text' class='form-control input-lg' placeholder='' name='no_po' Readonly = true value='".sprintf('%03s',$awal)."/$b/CMT/$years'>";
}
else{   
    echo"<input type='text' class='form-control input-lg' placeholder='' name='no_po' Readonly = true value='".sprintf('%03s',$potong)."/$b/CMT/$years'>";
}

I need suggestions, how to I can create this condition.

Thanks in advance.

Answer 1

AUTO_INCREMENT is meant for use with keys. If you want a value to start over, you will have to keep track yourself. If you have a really specific table with an AUTO_INCREMENT column set as key for month only:

CREATE TABLE myMonth(
month_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY);

Then you could use the modulus/remainder:

month=month_id%12+1;

Which will return the month for you (the +1 is to correct for the fact that the modulus will remainder of value-ROUND_DOWN(value/12)*12, which will be zero if the value is a multiple of 12, and a calendar has 1 as the first month (Pretty much except in Java where somebody decided that 0 was a nice number of month))