Model/ResourceModel/Contact.php
public function deleteContactIds()
    {
        $conn = $this->getConnection();
        $num = $conn->update(
            $this->getTable(Schema::EMAIL_CONTACT_TABLE),
            ['contact_id' => $this->expressionFactory->create(["expression" => 'null'])],
            $conn->quoteInto(
                'contact_id is ?',
                $this->expressionFactory->create(["expression" => 'not null'])
            )
        );

        return $num;
    }
public function deleteContactIds()
    {
        $conn = $this->getConnection();
        $num = $conn->update(
            $this->getTable(Schema::EMAIL_CONTACT_TABLE),
            ['contact_id' => $this->expressionFactory->create(["expression" => 'null'])],
            $conn->quoteInto(
                'contact_id is ?',
                $this->expressionFactory->create(["expression" => 'not null'])
            )
        );

        return $num;
    }
public function deleteContactIds ( ) { $ conn = $ this -> getConnection ( ) ; $ num = $ conn -> update ( $ this -> getTable ( Schema :: EMAIL_CONTACT_TABLE ) , [ 'contact_id' => $ this -> expressionFactory -> create ( [ "expression" => 'null' ] ) ] , $ conn -> quoteInto ( 'contact_id is ?' , $ this -> expressionFactory -> create ( [ "expression" => 'not null' ] ) ) ) ; return $ num ; }
Remove all contact_id from the table.

@return int
Remove all contact_id from the table .