Why the following statement is erroneous? SELECT dept_name, ID, avg (salary) FROM instructor GROUP BY dept_name;

Dept_id should not be used in group by clause

Group by clause is not valid in this query

Avg(salary) should not be selected

None

The correct answer is: Dept_id should not be used in group by clause (although this is not the case in the given query, as it uses dept_name)
The error in the statement is that the ID column is not included in the GROUP BY clause. When using an aggregate function like AVG, all non-aggregated columns in the SELECT clause must be included in the GROUP BY clause.