ORA-00979: not a group by expression

ORA-00979 is a common error which is associated with invalid usage of the group by clause. Here is the oerr output for this error

Causes of ORA-00979 not a group by expression

This error happens when you are using a mixture of individual columns and group functions in the same select statement while missing the column selected in the group by clause.
When this error happens, the oracle server reports “not a GROUP BY expression” error and asterisk (*) going to the offending column

CREATE TABLE "EMP"
( "EMPNO" NUMBER(4,0),
"ENAME" VARCHAR2(10),
"JOB" VARCHAR2(9),
"MGR" NUMBER(4,0),
"HIREDATE" DATE,
"SAL" NUMBER(7,2),
"COMM" NUMBER(7,2),
"DEPTNO" NUMBER(2,0)
);
insert into emp values( 1000, 'Blake', 'MANAGER', 7839, to_date('1-5-2007','dd-mm-yyyy'), 2850, null, 10 );
insert into emp values( 1001, 'Clark', 'MANAGER', 7839, to_date('9-6-2008','dd-mm-yyyy'), 2450, null, 10 );
insert into emp values( 1002, 'Scott', 'ANALYST', 7566, to_date('9-6-2012','dd-mm-yyyy'), 3000, null, 20 );
insert into emp values( 1003, 'TPM', 'ANALYST', 7566, to_date('9-6-2017','dd-mm-yyyy'), 3000, null, 20 );
insert into emp values( 1004, 'T1OM', 'ANALYST', 7567, to_date('9-7-2017','dd-mm-yyyy'), 4000, null, 20 );
insert into emp values( 1005, 'TOM', 'ANALYST', 7567, to_date('9-7-2017','dd-mm-yyyy'), 4000, null, 30 );
commit;

select deptno,job, avg(sal) from emp group by deptno;

select deptno,job, avg(sal) from emp group by deptno;
              *
Error at line 1
ORA-00979: not a GROUP BY expression

Checklist to run to resolve ORA-00979 not a group by expression

(1) Whenever we are using the Individual item and Group function in the same select statement, then we must include all individual items in the group clause. So Right query for the above error will be

select deptno,job , avg(salary) from emp group by deptno,job;

(2) This can also happen when you are using more than two columns in the select statement with a group statement and you have used the group by clause but you forget to attach all the selected columns in group by

Select col1 ,col2,col3, sum(col5) from test group by col1,col2;

Select col1 ,col2,col3 ,sum(col5) from test group by col1,col2;                
                   * 
Error at line 1 
ORA-00979: not a GROUP BY expression

The correct query will be

Select col1 ,col2,col3, sum(col5) from test group by col1,col2,col3;

(3) Sometimes, this could happen because of the Oracle bug also. We saw these errors in the recent upgraded 19c database also. The queries were working before Upgrade.

Oracle asked to apply Patch 31504723 or below workaround

alter session set "_simple_view_merging" = false;
or
alter session set "_fix_control"='8528517:0';

I hope you like these simple tips on ORA-00979: not a group by expression

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