public function unique($column, $keyConstraint = '')
    {
        $alter = '';
        $alter = static::ALTER_TABLE.' `'.$this->tableName.'` ADD ';

        if (is_array($column)) {
            // build query unique key for multiple columns
            $columns = $this->commands($column);

            $this->schema = $alter.' CONSTRAINT
            UC_'.strtoupper($this->tableName).'_'.strtoupper($keyConstraint).'_ID
            '.strtoupper(__FUNCTION__).' ('.$columns.')';
        }

        if (is_string($column)) {
            $this->schema = $alter.' '.strtoupper(__FUNCTION__).' ('.$column.');';
        }

        return $this;
    }