在插入语句中使用case

我正在尝试使用 case 插入

这是我使用的代码,但是

elseif ( exists(select id from transactions where tel = last_inserted_number && secure_using_payslip IS NULL)) then
    update transactions set secure_using_payslip=last_inserted_message where 
     tel=last_inserted_number;

     insert into messageout(messagetext, messageto)
        values("you choose not to secure with payslip.", last_inserted_number),(case when last_inserted_message = 'no');

     insert into messageout(messagetext, messageto)
        values("you choose to secure with payslip.", last_inserted_number),(case when last_inserted_message = 'yes');

       insert into messageout(messagetext, messageto)
        values("Are you formally employed or self employed?.", last_inserted_number);

代码失败。我应该如何在这里使用case?。