Retrieve specific fields from an attachment when only a value is known.

functions.php

function codepotent_get_attachment_field($select, $where, $value) {

	// Bring database object into scope.
	global $wpdb;

	// Assemble the query.
	$sql = "SELECT %s FROM $wpdb->posts WHERE %s='%s';";

	// Run the query.
	$result = $wpdb->get_var($wpdb->prepare($sql, $select, $where, trim($value)));

	// Error or empty result? Bail.
	if (is_wp_error($result) || empty($result)) {
		return 0;
	}

	// Return the value.
	return $result;

}

// Scenario: you need to find the ID of an image that was uploaded through 
// the ClassicPress media uploader, but, only have the URL of the full image.

// Solution: return the ID field where guid matches the image URL.
$select = 'ID';
$where = 'guid';
$value = 'https://codepotent.com/wp-content/uploads/2019/07/valves-at-factory.jpg';
$attachment_id = codepotent_get_attachment_field($select, $where, $value);