1Z0-006 SQL Fundamentals & Data Manipulation 5

Question 1

Which clause in a SELECT statement is used to combine rows from two or more tables based on a related column?

Accepted Answer

JOIN ... ON

Answer

JOIN ... ON links two tables by matching rows where the ON condition is true, producing a combined result set.

Question 2

What does ROLLBACK do in Oracle SQL?

Accepted Answer

Undoes all uncommitted DML changes since the last COMMIT or SAVEPOINT

Answer

ROLLBACK reverses all uncommitted DML operations back to the last COMMIT or to a named SAVEPOINT.

Question 3

Which SQL operator returns rows that exist in the first SELECT result but NOT in the second?

Accepted Answer

MINUS

Answer

Oracle's MINUS operator returns distinct rows from the first query that do not appear in the second query's result.

Question 4

Which of the following correctly adds a new column named phone_num to an existing table?

Accepted Answer

ALTER TABLE employees ADD phone_num VARCHAR2(20);

Answer

ALTER TABLE ... ADD is the DDL syntax used to add a new column to an existing table.

Question 5

What value does AVG(salary) return if a group contains salaries 1000, 2000, NULL, and 3000?

Accepted Answer

2000

Answer

AVG ignores NULL values, so it divides the sum (6000) by the count of non-NULL values (3), returning 2000.

(1Z0-006) Oracle Database Foundations Associate Practice Test