Oracle SQL Oracle SQL DDL and Schema Objects 1

Question 1

Which Oracle SQL constraint ensures no two rows in a table have the same value in a column?

Accepted Answer

UNIQUE

Answer

A UNIQUE constraint prevents duplicate values in a column or combination of columns, but unlike PRIMARY KEY, it allows NULL values.

Question 2

What does the CASCADE option do in DROP TABLE in Oracle SQL?

Accepted Answer

Drops the table and all dependent foreign key constraints

Answer

DROP TABLE ... CASCADE CONSTRAINTS removes the table along with all foreign key constraints that reference it.

Question 3

Which Oracle SQL statement modifies the structure of an existing table?

Accepted Answer

ALTER TABLE

Answer

ALTER TABLE is used to add, modify, or drop columns and constraints in an existing table without recreating it.

Question 4

Which Oracle SQL object automatically generates unique sequential numbers?

Accepted Answer

SEQUENCE

Answer

A SEQUENCE is a database object that generates unique integer values, commonly used as surrogate primary keys.

Question 5

What is the purpose of a DATABASE LINK in Oracle SQL?

Accepted Answer

Allows queries to access objects in a remote Oracle database

Answer

A database link (DBLINK) enables Oracle to connect to and query objects in another Oracle database as if they were local.

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