Magento 2 – Get Product Image Using Helper and Block

you can do it this way, but you have to extend the original helper, because all classes that use it, actually expect an instance of the original helper (or a derived class)

If you want to use SQL approach, You can use the following standalone script which can be run either via Web or CLI

<?php
/**
 *
 * @author Raj KB<magepsycho@gmail.com>
 * @website http://www.magepsycho.com
 * @extension MassImporterPro: Pricing - http://www.magepsycho.com/mass-importer-pro-price-importer-regular-special-tier-group.html
 */
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

// Capture warning / notice as exception
set_error_handler('ctv_exceptions_error_handler');
function ctv_exceptions_error_handler($severity, $message, $filename, $lineno) {
    if (error_reporting() == 0) {
        return;
    }
    if (error_reporting() & $severity) {
        throw new ErrorException($message, 0, $severity, $filename, $lineno);
    }
}

require __DIR__ . '/../app/bootstrap.php';
$bootstrap = \Magento\Framework\App\Bootstrap::create(BP, $_SERVER);

$obj = $bootstrap->getObjectManager();

$state = $obj->get('Magento\Framework\App\State');
$state->setAreaCode('adminhtml');


/**************************************************************************************************/
// UTILITY FUNCTIONS - START
/**************************************************************************************************/
function _mpLog($data, $includeSep = false)
{
    $fileName = BP . '/var/log/m2-magepsycho-import-prices.log';
    if ($includeSep) {
        $separator = str_repeat('=', 70);
        file_put_contents($fileName, $separator . '<br />' . PHP_EOL,  FILE_APPEND | LOCK_EX);
    }
    file_put_contents($fileName, $data . '<br />' .PHP_EOL,  FILE_APPEND | LOCK_EX);
}

function mpLogAndPrint($message, $separator = false)
{
    _mpLog($message, $separator);
    if (is_array($message) || is_object($message)) {
        print_r($message);
    } else {
        echo $message . '<br />' . PHP_EOL;
    }

    if ($separator) {
        echo str_repeat('=', 70) . '<br />' . PHP_EOL;
    }
}

function getIndex($field)
{
    global $headers;
    $index = array_search($field, $headers);
    if ( !strlen($index)) {
        $index = -1;
    }
    return $index;
}

function readCsvRows($csvFile)
{
    $rows = [];
    $fileHandle = fopen($csvFile, 'r');
    while(($row = fgetcsv($fileHandle, 0, ',', '"', '"')) !== false) {
        $rows[] = $row;
    }
    fclose($fileHandle);
    return $rows;
}

function _getResourceConnection()
{
    global $obj;
    return $obj->get('Magento\Framework\App\ResourceConnection');
}

function _getReadConnection()
{
    return _getConnection('core_read');
}

function _getWriteConnection()
{
    return _getConnection('core_write');
}

function _getConnection($type = 'core_read')
{
    return _getResourceConnection()->getConnection($type);
}

function _getTableName($tableName)
{
    return _getResourceConnection()->getTableName($tableName);
}

function _getAttributeId($attributeCode)
{
    $connection = _getReadConnection();
    $sql = "SELECT attribute_id FROM " . _getTableName('eav_attribute') . " WHERE entity_type_id = ? AND attribute_code = ?";
    return $connection->fetchOne(
        $sql,
        [
            _getEntityTypeId('catalog_product'),
            $attributeCode
        ]
    );
}

function _getEntityTypeId($entityTypeCode)
{
    $connection = _getConnection('core_read');
    $sql        = "SELECT entity_type_id FROM " . _getTableName('eav_entity_type') . " WHERE entity_type_code = ?";
    return $connection->fetchOne(
        $sql,
        [
            $entityTypeCode
        ]
    );
}

function _getIdFromSku($sku)
{
    $connection = _getConnection('core_read');
    $sql        = "SELECT entity_id FROM " . _getTableName('catalog_product_entity') . " WHERE sku = ?";
    return $connection->fetchOne(
        $sql,
        [
            $sku
        ]
    );

}

function checkIfSkuExists($sku)
{
    $connection = _getConnection('core_read');
    $sql        = "SELECT COUNT(*) AS count_no FROM " . _getTableName('catalog_product_entity') . " WHERE sku = ?";
    return $connection->fetchOne($sql, [$sku]);
}

function updatePrices($sku, $price, $storeId = 0)
{
    $connection     = _getWriteConnection();
    $entityId       = _getIdFromSku($sku);
    $attributeId    = _getAttributeId('price');

    $sql = "INSERT INTO " . _getTableName('catalog_product_entity_decimal') . " (attribute_id, store_id, entity_id, value) VALUES (?, ?, ?, ?) ON DUPLICATE KEY UPDATE value=VALUES(value)";
    $connection->query(
        $sql,
        [
            $attributeId,
            $storeId,
            $entityId,
            $price
        ]
    );
}

/**************************************************************************************************/
// UTILITY FUNCTIONS - END
/**************************************************************************************************/

try {
    $csvFile        = 'var/import/prices.csv'; #EDIT - The path to import CSV file (Relative to Magento2 Root)
    $csvData        = readCsvRows(BP . '/' . $csvFile);
    $headers        = array_shift($csvData);

    $count   = 0;
    foreach($csvData as $_data) {
        $count++;
        $sku   = $_data[getIndex('sku')];
        $price = $_data[getIndex('price')];

        if ( ! checkIfSkuExists($sku)) {
            $message =  $count .'. FAILURE:: Product with SKU (' . $sku . ') doesn\'t exist.';
            mpLogAndPrint($message);
            continue;
        }

        try {
            updatePrices($sku, $price);
            $message = $count . '. SUCCESS:: Updated SKU (' . $sku . ') with price (' . $price . ')';
            mpLogAndPrint($message);
        } catch(Exception $e) {
            $message =  $count . '. ERROR:: While updating  SKU (' . $sku . ') with Price (' . $price . ') => ' . $e->getMessage();
            mpLogAndPrint($message);
        }
    }
} catch (Exception $e) {
    mpLogAndPrint(
        'EXCEPTION::' . $e->getTraceAsString()
    );
}

And the sample CSV can be used as:

"sku","price"
"24-MB01","31"
"24-MX02","32"
"24-UG04","94"
"24-UG05","99"

Source: http://bit.ly/M2-Bulk-Price-Update