My personal DB Class (Including Singleton)

Singleton Database Class.php

<?php
# v2.2
class dbM {
    private static $pdo;
    private static $instance;

    private function __construct() {
    }

    public static function init() {
        if (!isset(self::$instance)) {
            $c = __CLASS__;
            self::$instance = new $c;

            try {
                self::$pdo = new PDO(
                    'mysql:host=localhost;dbname=' . DB_NAME . ';charset=UTF8',
                    DB_USER,
                    DB_PASS,
                    [
                        PDO::ATTR_EMULATE_PREPARES => false,
                        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
                        PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
                    ]
                );
            } catch (\Throwable $th) {
                //throw $th;
            }
        }

        return self::$instance;
    }

    public static function fetch($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->fetch();
    }

    public static function fetchColumn($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->fetchColumn();
    }

    public static function fetchAll($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->fetchAll();
    }

    public static function fetchAllColumn($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->fetchAll(PDO::FETCH_COLUMN);
    }

    public static function fetchKeyPair($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->fetchAll(PDO::FETCH_KEY_PAIR);
    }

    public static function fetchKeyPairs($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->fetchAll(PDO::FETCH_GROUP | PDO::FETCH_COLUMN);
    }

    public static function fetchGroup($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->fetchAll(PDO::FETCH_GROUP);
    }

    public static function exist($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->rowCount() ? true:false;
    }

    public static function rowCount($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->rowCount();
    }

    public static function query($sql, $params = null) {
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($params);

        return $stmt->rowCount();
    }

    public static function insert($tblName, $insertItems, $ignore = false) {
        $sql = self::queryBuilder($tblName, $insertItems, $ignore);
        
        $stmt = self::$pdo->prepare($sql);
        $stmt->execute($insertItems);

        return self::$pdo->lastInsertId();
    }

    /*
        insertMany(
            'my_table',
            [ 'col1', 'col2' ],
            [
                [ 'col1_val_1', 'col2_val_1' ],
                [ 'col1_val_2', 'col2_val_2' ],
                [ 'col1_val_3', 'col2_val_3' ]
            ]
        )
    */
    public static function insertMany($tableName, $columns, $values, $ignore = false) {
        $params = [];
        $query = $ignore ?
            "INSERT IGNORE INTO `${tableName}` (":
            "INSERT INTO `${tableName}` (";
        $columnsString = '';
        foreach ($columns as $column) {
            $columnsString .= '`' . $column . '`,';
        }
        $columnsString = rtrim($columnsString, ',');
        $query .= $columnsString . ') VALUES ';

        $valuesString = '';
        foreach ($values as $value) {
            $valuesString .= '(';
            foreach ($value as $col) {
                $valuesString .= "?,";
                $params[] = $col;
            }
            $valuesString = rtrim($valuesString, ',');
            $valuesString .= '),';
        }
        $valuesString = rtrim($valuesString, ',');

        $query .= $valuesString;

        return self::query($query, $params);
    }

    private static function queryBuilder($tblName, $insertItems, $ignore) {
        $ignore = $ignore? 'IGNORE':'';
        $c = '';
        $v = '';
        foreach ($insertItems as $key => $value) {
            $c .= '`' . $key . '`,';
            $v .= ':' . $key . ',';
        }
        $c = rtrim($c, ',');
        $v = rtrim($v, ',');
        $finalQuery = "INSERT {$ignore} INTO `{$tblName}` ({$c}) VALUES ({$v})";

        return $finalQuery;
    }
}
dbM::init();