Case function with the count condition - sql

Question

I'm using the case function to highlight the current scenario of my task running in my system, where the task status is Completed, Failed or Waiting.
I got the case function to use for Completed and Failed since it was just a one-line command. But for the Waiting state, I would like to build the condition with the count in the case function.
Currently, I'm using the syntax for waiting for the state
CASE WHEN task_Status='Waiting'
and Count(Task_Status) > 30
THEN "More task are in Waiting State"
But the Count Function is giving me ERROR, Requesting the assistance on the same. Thanks in Advance.

Answer 1

It would have been nice if you posted sample data. As you didn't have a look at the following example based on Scott's schema. Instead of your status column, I'm counting clerks in every department.
SQL> select deptno, ename, job from emp order by deptno, job;
DEPTNO ENAME JOB
---------- ---------- ---------
10 MILLER CLERK --> 1 clerk in department 10
10 CLARK MANAGER
10 KING PRESIDENT
20 SCOTT ANALYST
20 FORD ANALYST
20 ADAMS CLERK --> 2 clerks in
20 SMITH CLERK --> department 20
20 JONES MANAGER
30 JAMES CLERK --> 1 clerk in department 30
30 BLAKE MANAGER
30 MARTIN SALESMAN
30 WARD SALESMAN
30 ALLEN SALESMAN
30 TURNER SALESMAN
14 rows selected.
SQL>
This is what you're trying to do now:
SQL> select deptno,
2 case when job = 'CLERK' and count(*) > 1 then
3 'More than a single clerk in department'
4 else
5 'Only one clerk in department'
6 end status
7 from emp
8 group by deptno;
case when job = 'CLERK' and count(*) > 1 then
*
ERROR at line 2:
ORA-00979: not a GROUP BY expression
SQL>
If we include the job column, error goes away, but - result isn't what we expected:
SQL> select deptno,
2 case when job = 'CLERK' and count(*) > 1 then
3 'More than a single clerk in department'
4 else
5 'Only one clerk in department'
6 end status
7 from emp
8 group by deptno, job
9 order by deptno;
DEPTNO STATUS
---------- --------------------------------------
10 Only one clerk in department
10 Only one clerk in department
10 Only one clerk in department
20 Only one clerk in department
20 More than a single clerk in department
20 Only one clerk in department
30 Only one clerk in department
30 Only one clerk in department
30 Only one clerk in department
9 rows selected.
SQL>
What to do? Don't count - sum!
SQL> select
2 deptno,
3 case when sum(case when job = 'CLERK' then 1 else 0 end) > 1 then
4 'More than a single clerk in department'
5 else
6 'Only one clerk in department'
7 end status
8 from emp
9 group by deptno
10 order by deptno;
DEPTNO STATUS
---------- --------------------------------------
10 Only one clerk in department
20 More than a single clerk in department
30 Only one clerk in department
SQL>
In your case, that would be
case when sum(case when task_status = 'Waiting' then 1 else 0 end) > 30 then
'More tasks are in Waiting State'
end
Note that strings should be enclosed into single, not double quotes.