每次在php中插入新数据时，求和一个字符串

I have a variable(database column value) which value is look like below.

ALI-0001

now i wanna auto increment this code like ALI-0002, ALI-0003,ALI-0004,ALI-0005 every time i insert new data. I tried the following code.

$project_code = $a[0]->project_code;
$integer = (integer) substr($max_issue_number, 4);
$sum = $integer+1;
$issue_number = $project_code.'-000'.$sum;

Your solution is str_pad ref: http://php.net/manual/en/function.str-pad.php

So your code should be as below:

$issue_number = $project_code.'-'.str_pad($sum, 4, '0', STR_PAD_LEFT);