Use of Single Quotes Before Column Name Oracle
<p>I am told to edit existing codes which was written five years ago by five different programmers and I found single quotation marks just right before the name of a column in some query. What is the use of it? I never used Oracle database before... The part of the query looked like this <code>' ' work_instance</code>, half of the code is just like below :</p>

<pre><code>select PR.request_id, 
       PR.investor_id, 
       PR.proposal_date,
       ' ' work_instance,    
       INV.foreign_company_name name,  
       PR.is_remove_cancel,   
       PR.remove_cancel_number,
       PR.status_id, 
       REFR.description, 
       PR.fo_id, 
       PR.staff_id, 
       PR.case_id,
       PR.sub_department_head_id, 
       PR.director_id, 
       ROUND((sysdate-PR.proposal_date)) as processing_time 
from REMOVAL.request PR,
     KPPA.foreign_company_kp INV,
     REMOVAL.ref_t_status_workflow REFR 
where ...criteria here...
</code></pre>

<p>Thank you for all of your help, wish you all the best!</p>