如何通过在数据库

Question

假设在数据库中我有一个值2300，我想为它添加200，我有以下PHP脚本

$to_add = 200;
$query = mysqli_query("select * from table where id = '$row'");
$rec = mysqli_fetch_assoc($query);
$old_number = $rec['col'];
$new_number = $old_number + $to_add;
$query1 = mysqli_query("update table set col = '$new_number' where id = '$row' ");

我的问题是，我们可以使用单个查询完成上述任务，例如

$new_number = 200;
$query = mysqli_query("update table set col = 'pre_value + $new_number' where id = '$row' ");

Answer 1

还可以使用速记赋值运算符

$new_number = 200; $query = mysqli_query("update table set col +=
$new_number where id = '$row'");

Answer 2

试试这个：

$new_number = 200;
$query = mysqli_query("update table set col = col + $new_number where id = '$row' ");

Answer 3

$new_number = 200;

update table set col = col + $new_number where id = '$row';