您可以在表单请求中创建自定义验证规则，并在规则本身中执行DB查询。
您可以创建自定义验证规则并在规则中使用

public function rules()
{
    return [
        'input_value' => ['required', new ValidCustomInputRule]
    ];
}

您可以使用php artisan make：rule ValidCustomInputRule来制作它

use Illuminate\Contracts\Validation\Rule;
use Illuminate\Support\Facades\DB;

    class ValidCustomInputRule implements Rule
    {
        public function passes($attribute, $value)
        {
            $sum = DB::table('table_name')->sum('column_name');
    
            return $value <= $sum;
        }
    
        public function message()
        {
            return 'The input value is greater than the sum of the column in the database.';
        }
    }

我认为如果你想把所有的信息都保存在你的表单请求中，你可以使用闭包。

class YourFormRequest extends FormRequest
{
    public function rules(): array
    {
        return [
            'input_name' => [
                'required',
                'numeric',
                function (string $attribute, mixed $value, Closure $fail) {
                    $max = DB::table('table-table')->sum('column');

                    if ($value > $max) {
                        $fail("$attribute cannot be more than $max.");
                    }
                },
            ],
        ];
    }
}

如果这不起作用，我想您可以将其添加到after钩子中。

use Illuminate\Validation\Validator;

class YourFormRequest extends FormRequest
{
    public function rules(): array
    {
        return [
            'input_name' => [
                'required',
                'numeric',
            ],
        ];
    }

    public function withValidator(Validator $validator): void
    {
        $validator->after(function (Validator $validator) {
            $value = $validator->getData()['input_name'];
            $max = DB::table('table-table')->sum('column');

            if ($value > $max) {
                $validator->errors()->add('input_name', "input_name cannot be more than $max");
            }
        });
    }
}