1Z0-071 Set Operators 3

Question 1

When using set operators, which columns must have compatible data types between the two SELECT statements?

Accepted Answer

All corresponding columns in both SELECT statements

Answer

Only the first column in each SELECT statement

Answer

Only the primary key columns

Answer

Only columns appearing in the WHERE clause

Question 2

Which of the following is NOT a valid set operator in Oracle SQL?

Accepted Answer

INTERSECT ALL

Answer

UNION

Answer

UNION ALL

Answer

MINUS

Question 3

What is the result of the following query: SELECT 1 FROM DUAL UNION SELECT 1 FROM DUAL?

Accepted Answer

Returns one row containing the value 1

Answer

Returns two rows each containing the value 1

Answer

Returns an error because DUAL cannot be referenced twice

Answer

Returns NULL

Question 4

In a compound query using set operators, an ORDER BY clause can reference output columns using which methods?

Accepted Answer

Column aliases from the first SELECT or position numbers

Answer

Column aliases defined in the first SELECT statement only

Answer

Position numbers such as ORDER BY 1, 2 only

Answer

Table-qualified column names such as emp.salary

Question 5

Why is UNION generally slower in performance compared to UNION ALL?

Accepted Answer

UNION requires an additional sort and deduplication step to eliminate duplicate rows

Answer

UNION ALL fetches fewer rows from the database storage

Answer

UNION performs more join operations internally

Answer

UNION ALL uses a different execution plan that avoids full table scans

Question 6

A business analyst needs to find all product IDs that appeared in January sales but did NOT appear in February sales. Which set operator is most appropriate?

Accepted Answer

MINUS

Answer

UNION

Answer

UNION ALL

Answer

INTERSECT

Question 7

Which of the following correctly describes how set operators handle NULL values when comparing rows?

Accepted Answer

Set operators treat two NULL values as equal when determining row matches

Answer

NULL values are ignored and never returned by any set operator

Answer

Set operators always convert NULL to zero before comparing

Answer

NULL values cause an ORA-01400 error in set operator queries