ExpressionField::removeSubqueries

static function removeSubqueries($expression)
{
	// remove double slashes
	$expression = str_replace('\\\\\\\\', '', $expression);

	// remove strings
	$expression = static::removeStrings('"', $expression);
	$expression = static::removeStrings("'", $expression);

	// remove subqueries' bodies
	$clear = static::removeSubqueryBody($expression);

	while ($clear !== $expression)
	{
		$expression = $clear;
		$clear = static::removeSubqueryBody($expression);
	}

	return $clear;
}