1Z0-071 Joining Multiple Tables 2

Question 1

What is a self-join used for?

Accepted Answer

Joining a table to itself to compare rows within the same table

Answer

A self-join joins a table to itself using aliases, typically to compare rows such as employee-manager relationships.

Question 2

In a three-table join, how many join conditions are typically required?

Accepted Answer

2

Answer

For N tables you need at minimum N-1 join conditions, so 3 tables require at least 2 join conditions.

Question 3

Which Oracle-proprietary outer join syntax uses the (+) operator?

Accepted Answer

SELECT * FROM a, b WHERE a.id = b.id(+)

Answer

Oracle's proprietary outer join syntax places (+) on the side of the table that may have missing rows (the optional side).

Question 4

Which type of join condition compares columns using an operator other than equals (=)?

Accepted Answer

Non-equijoin

Answer

A non-equijoin uses comparison operators like BETWEEN, <, or > instead of = to match rows.

Question 5

When using a USING clause in a JOIN, what happens if you try to prefix the USING column with a table alias?

Accepted Answer

Oracle raises an ORA-25154 error

Answer

Oracle raises ORA-25154 if you prefix the USING clause column with a table alias because it is common to both tables.

1Z0-071 - Oracle Database SQL Certified Associate Practice Test