Date Difference and ORA-00937 - not a single-group group function

Question

I am trying to add two tables and get the total days from two dates. But having the following simple issue: not a single-group group function .

This is what I've tried so far:

SELECT COUNT(status) AS "Present Days",  
       (SELECT TRUNC(TO_DATE('01/10/2018', 'MM/DD/YYYY') - TO_DATE(k.JOINING_DATE, 'MM/DD/YYYY')) 
        FROM attendance m
             INNER JOIN EMP_OFFICIAL k 
             ON k.EMPNO = m.EMPNO 
        WHERE m.empno='EMP00254' 
        AND m.status='P') AS "Total Days" 
FROM attendance 
WHERE empno = 'EMP00254' 
AND status = 'P';

Can I get the days without using the DUAL?

Answer 1

First off, that subquery is most likely not scalar (it looks like you're assuming multiple rows can come from the attendance table) and second, it contains an unnecessary join..

What I would do instead is something like:

select count(*) as "Present Days",
       to_date('01/10/2018', 'mm/dd/yyyy') - k.joining_date "Total Days"
from   attendance a
       inner join emp_official k on a.empno = k.empno
where  a.empno = 'EMP00254'
and    a.status = 'P'
group by to_date('01/10/2018', 'mm/dd/yyyy') - k.joining_date;

This does assume that the k.joining_date column is of DATE datatype and that 'k.empno' is a unique column.

Answer 2

If there is only one row in the EMP_OFFICIAL table for each employee then you could do:

SELECT COUNT(a.status) AS "Present Days",  
       TRUNC( SYSDATE ) - TRUNC( MIN( k.joining_date ) ) AS "Total Days" 
FROM   attendance a
       RIGHT OUTER JOIN EMP_OFFICIAL k
       ON ( k.EMPNO = a.EMPNO )
WHERE  a.empno = 'EMP00254' 
WHERE  a.status = 'P';

or you could do the aggregation in a sub-query:

SELECT a."Present Days",  
       TRUNC( SYSDATE ) - TRUNC( k.joining_date ) AS "Total Days" 
FROM   (
         SELECT EMPNO,
                COUNT( status ) AS "Present Days"
         FROM   attendance
         WHERE  EMPNO = 'EMP00254'
         AND    status = 'P'
         GROUP BY EMPNO
       ) a
       RIGHT OUTER JOIN EMP_OFFICIAL k
       ON ( k.EMPNO = a.EMPNO )
WHERE  k.EMPNO = 'EMP00254';

Or you could use UNION ALL to query the two tables and have the result in two rows (rather than two columns):

SELECT 'Present Days' As type,
       COUNT(status)  AS Days
FROM   attendance
WHERE  empno = 'EMP00254' 
WHERE  status = 'P'
UNION ALL
SELECT 'Total Days',
       TRUNC( SYSDATE ) - TRUNC( joining_date )
FROM   EMP_OFFICIAL
WHERE  empno = 'EMP00254';

Answer 3

Either remove COUNT(status) AS "Present Days" part and SELECT inside paranthesis :

SELECT (TRUNC(TO_DATE('01/10/2018', 'MM/DD/YYYY') - TO_DATE(k.JOINING_DATE, 'MM/DD/YYYY')) "time difference" FROM attendance m
INNER JOIN EMP_OFFICIAL k ON k.EMPNO = m.EMPNO where m.empno='EMP00254' and m.status='P') AS "Total Days" 
 FROM attendance where empno = 'EMP00254' and status = 'P';

OR

use the following (add GROUP BY expression at the end of sql):

SELECT COUNT(status) AS "Present Days",  
(TRUNC(TO_DATE('01/10/2018', 'MM/DD/YYYY') - TO_DATE(k.JOINING_DATE, 'MM/DD/YYYY')) "time difference" FROM attendance m
INNER JOIN EMP_OFFICIAL k ON k.EMPNO = m.EMPNO where m.empno='EMP00254' and m.status='P') AS "Total Days" 
 FROM attendance where empno = 'EMP00254' and status = 'P'
GROUP BY (TRUNC(TO_DATE('01/10/2018', 'MM/DD/YYYY') - TO_DATE(k.JOINING_DATE, 'MM/DD/YYYY'));

Since , groupped and non-groupped items can not be used together.

By the way, you don't need to use dual in your inline select statement like ( SELECT TRUNC(TO_DATE('01/10/2018', 'MM/DD/YYYY') - TO_DATE(k.JOINING_DATE, 'MM/DD/YYYY') FROM DUAL ) , just ( TRUNC(TO_DATE('01/10/2018', 'MM/DD/YYYY') - TO_DATE(k.JOINING_DATE, 'MM/DD/YYYY')) is enough.