public function colConstraint(/*# string */ $string)
    {
        $col = &$this->col_defs[count($this->col_defs) - 1];
        if (!isset($col['constraint'])) {
            $col['constraint'] = [];
        }
        $con = &$col['constraint'];
        $con[] = $string;
        return $this;
    }
public function colConstraint(/*# string */ $string)
    {
        $col = &$this->col_defs[count($this->col_defs) - 1];
        if (!isset($col['constraint'])) {
            $col['constraint'] = [];
        }
        $con = &$col['constraint'];
        $con[] = $string;
        return $this;
    }
{@inheritDoc}