Error logging in a database is in Yii2 really not comfortably implemented. (My opinion). The additional row with the server information confused and is not good to read. Here's a small class, which makes sure that the prefix matches the URL name (if not available, the user IP) and adds the additional informations in the message.

CleanDBLogger.php

<?php


namespace app\lib;


use yii\helpers\VarDumper;
use yii\log\DbTarget;
use yii\log\LogRuntimeException;

class MyDBLogger extends DbTarget
{
    public function export()
    {
        if ($this->db->getTransaction()) {
            // create new database connection, if there is an open transaction
            // to ensure insert statement is not affected by a rollback
            $this->db = clone $this->db;
        }

        $tableName = $this->db->quoteTableName($this->logTable);
        $sql = "INSERT INTO $tableName ([[level]], [[category]], [[log_time]], [[prefix]], [[message]])
                VALUES (:level, :category, :log_time, :prefix, :message)";
        $command = $this->db->createCommand($sql);
        foreach ($this->messages as $message) {
            list($text, $level, $category, $timestamp) = $message;
            if (!is_string($text)) {
                // exceptions may not be serializable if in the call stack somewhere is a Closure
                if ($text instanceof \Throwable || $text instanceof \Exception) {
                    $text = (string) $text;
                } else {
                    $text = VarDumper::export($text);
                }
            }


            //collect additional infos
            $additional = [];
            if(isset($_SERVER)){ //looks cleaner :)
                $additional["SERVER"] = $_SERVER;
            }
            if(isset($_GET)){ //CLI apps 
                $additional["GET"] = $_GET;
            }
            if(isset($_POST)){
                $additional["POST"] = $_POST;
            }

            if(count($additional)!==0){
                $text=$text."\n\n\n".VarDumper::export($additional);
            }


            if ($command->bindValues([
                    ':level' => $level,
                    ':category' => $category,
                    ':log_time' => $timestamp,
                    ':prefix' => $this->getMessagePrefix($message),
                    ':message' => $text,
                ])->execute() > 0) {
                continue;
            }
            throw new LogRuntimeException('Unable to export log through database!');
        }
    }
}

log_config.php

return [

    //............

    /*
     * --------------------------------------------------------------------------
     * Log Targets
     * --------------------------------------------------------------------------
     *
     * A log target is an instance of the yii\log\Target class or its child class.
     * It filters the log messages by their severity levels and categories and then
     * exports them to some medium. You can register multiple targets.
     *
     */

    'targets' => [


        [
            'class' => 'app\lib\MyDBLogger', //your class
            'levels' => ['error'], //or ['warning','error']

            'logVars' => [], //we dont need this...
            'logTable' => 'log_front', // or another table...

            'prefix' => function ($message) {
                if(isset($_SERVER) && isset($_SERVER["REQUEST_URI"])){
                    return $_SERVER["REQUEST_URI"];
                }
                return $_SERVER["REMOTE_ADDR"];
            }
        ],


       //other targets
    ],
];