IF EXISTS condition not working with PLSQL

Question

I am trying to print the TEXT when condition is TRUE. The select code is perfectly working fine. It's showing 403 value when i only run select code. But I have to print some text when condition exists. What's the problem with following code.

BEGIN
IF EXISTS(
SELECT CE.S_REGNO FROM
COURSEOFFERING CO
JOIN CO_ENROLMENT CE
  ON CE.CO_ID = CO.CO_ID
WHERE CE.S_REGNO=403 AND CE.COE_COMPLETIONSTATUS = 'C' AND CO.C_ID = 803
)
THEN
    DBMS_OUTPUT.put_line('YES YOU CAN');
END;

Here is the error report:

Error report:
ORA-06550: line 5, column 1:
PLS-00103: Encountered the symbol "JOIN" when expecting one of the following:

   ) , with group having intersect minus start union where
   connect
06550. 00000 -  "line %s, column %s:\n%s"
*Cause:    Usually a PL/SQL compilation error.
*Action:

Solution 1

IF EXISTS() is semantically incorrect. EXISTS condition can be used only inside a SQL statement. So you might rewrite your pl/sql block as follows:

declare
  l_exst number(1);
begin
  select case 
           when exists(select ce.s_regno 
                         from courseoffering co
                         join co_enrolment ce
                           on ce.co_id = co.co_id
                        where ce.s_regno=403 
                          and ce.coe_completionstatus = 'C' 
                          and ce.c_id = 803
                          and rownum = 1
                        )
           then 1
           else 0
         end  into l_exst
  from dual;

  if l_exst = 1 
  then
    DBMS_OUTPUT.put_line('YES YOU CAN');
  else
    DBMS_OUTPUT.put_line('YOU CANNOT'); 
  end if;
end;

Or you can simply use count function do determine the number of rows returned by the query, and rownum=1 predicate - you only need to know if a record exists:

declare
  l_exst number;
begin
   select count(*) 
     into l_exst
     from courseoffering co
          join co_enrolment ce
            on ce.co_id = co.co_id
    where ce.s_regno=403 
      and ce.coe_completionstatus = 'C' 
      and ce.c_id = 803
      and rownum = 1;

  if l_exst = 0
  then
    DBMS_OUTPUT.put_line('YOU CANNOT');
  else
    DBMS_OUTPUT.put_line('YES YOU CAN');
  end if;
end;

Solution 2

Unfortunately PL/SQL doesn't have IF EXISTS operator like SQL Server. But you can do something like this:

begin
  for x in ( select count(*) cnt
               from dual 
              where exists (
                select 1 from courseoffering co
                  join co_enrolment ce on ce.co_id = co.co_id
                 where ce.s_regno = 403 
                   and ce.coe_completionstatus = 'C' 
                   and co.c_id = 803 ) )
  loop
        if ( x.cnt = 1 ) 
        then
           dbms_output.put_line('exists');
        else 
           dbms_output.put_line('does not exist');
        end if;
  end loop;
end;
/

Comments

[nirmalgyanwali]

Thank you Nicholas for your brilliant code. It perfectly work for me.

[nirmalgyanwali]

Thank you Hilton for your help. Ya, I got the idea from your code. But I don't know why the condition is FALSE and it's showing ELSE condition. The value in x.cnt is 0.

[HiltoN]

Probably this is because I lowercased your query with constant 'C', that should be in upper case.

[miracle_the_V]

"simply use count function" is much less efficient. Stick with exists/not exists.

[zygimantus]

Why exists cannot be used in insert statements?

[William Robertson]

exists certainly can be used with insert statements.