How to use exists function in sql query?

Question

Select EXISTS (adm.document_id) as documentUploaded, name,customer_id as customerId,
adm.id,document.id as documentId from 
document,application_document_mapping as adm where
document.deleted=false and document.id=adm.document_id and application_id=1;

The above query gives a syntax error. Not able to understand why?

Answer 1

below is an way

 select t1.* from table document t1
 where exists ( select 1 from application_document_mapping t2 where
                                      t1.id=t2.document_id 
                                      and application_id=1)

Answer 2

EXISTS is not a function. It has to contain a subquery, that is, something that starts with SELECT . EXISTS returns TRUE if the subquery has at least one result row, else FALSE .

You can either use EXISTS like in Zaynul's answer or use an outer join:

SELECT adm.document_id IS NULL AS documentuploaded,
       name,
       customer_id AS customerId,
       adm.id,
       document.id AS documentId
FROM document
   LEFT JOIN application_document_mapping AS adm
      ON document.id = adm.document_id AND adm.application_id = 1
WHERE NOT document.deleted;