如何在mysql中增加默认值

Question

mysql表中有一个字段(demo_field)(varchar)。我想用预定义的前缀来增加这个字段值。例如，我的字段第一个值是demo001。现在，当插入新的值时，我希望增加像demo002, demo003这样的数字。我怎样才能用PHP做到这一点。

Answer 1

试试这个-

//fetch data from table
$sql = $mysqli->query('select count(demo_field) as total,demo_field from tablename limit 1');
$res = $sql->fetch_assoc();

//generate string from existing data
$str = substr($res['demo_field'], 0, 4);
$dig = str_replace($str, '', $res['demo_field']);
$dig = $dig+$res['total'];

//add padding if needed
$dig = str_pad($dig, 3, '0', STR_PAD_LEFT);

//concatenate string & digits
$newStr = $str.$dig;

var_dump($newStr);

另一种不计数的方法

$sql = $mysqli->query('select max(demo_field) as demo_field from demo');
$res = $sql->fetch_assoc();

$str = substr($res['demo_field'], 0, 4);
$dig = str_replace($str, '', $res['demo_field']);
$dig += 1;
$dig = str_pad($dig, 3, '0', STR_PAD_LEFT);
$newStr = $str.$dig;

var_dump($newStr);

希望这可以解决count的问题。

另一种不加填充的字母数字字符串最大计数的解决方案-

$sql = $mysqli->query('select max(cast(substring(demo_field, 5) as unsigned)) as digit,     demo_field from demo');
$res = $sql->fetch_assoc();

$str = substr($res['demo_field'], 0, 4);
$dig = $res['digit'] + 1;
$newStr = $str.$dig;

var_dump($newStr);

Answer 2

//use PHP not mysql
$pre = 'demo';
$num = 0;
define('MAX', 100);
for($num = 0; $num < MAX; $num++)
{
    $pre_str = $pre . sprintf("%03d", $num);
    //insert here
}

Answer 3

您必须使用INT字段，并在“选择”时间将其转换为任何您想要的格式。

在MySQL中，我们不能将AutoIncrement用于Varchar。