Examine the description of the CUSTONERS tableCUSTON is the PRIMARY KEY.

To determine if customer details have been entered more than once using a different custno, the following methods can be used:

SUBQUERY: A subquery can be used to find duplicate names by grouping the names and having a count greater than one.

SELECT custname FROM customers GROUP BY custname HAVING COUNT(custname) > 1;

Self Join: A self join can compare rows within the same table to find duplicates in the custname column, excluding matches with the same custno.

SELECT c1.custname FROM customers c1 JOIN customers c2 ON c1.custname = c2.custname AND c1.custno != c2.custno;

These methods allow us to find duplicates in the custname column regardless of the custno. Options A, B, and E are not applicable methods for finding duplicates in this context.

References:

Oracle Documentation on Group By: Group By

Oracle Documentation on Joins: Joins