Which two statements are true about Oracle databases and SQL?
A.
Updates performed by a database user can be rolled back by another user by using the ROLLBACK command.
B.
The database guarantees read consistency at select level on user-created tablers.
C.
When you execute an UPDATE statement, the database instance locks each updated row.
D.
A query can access only tables within the same schema.
E.
A user can be the owner of multiple schemas In the same database.
The Answer Is:
B, C
This question includes an explanation.
Explanation:
B. True. Oracle databases guarantee read consistency at the transaction level, meaning that each query can only see data that has been committed before the query began executing.
C. True. When an UPDATE statement is executed, Oracle locks each row as it is updated to prevent other transactions from modifying it until the transaction is committed or rolled back.
A is incorrect because updates made by one user cannot be rolled back by another user. D is incorrect because a query can access tables in other schemas if proper permissions are granted. E is incorrect because a user can own only one schema, which has the same name as the user in an Oracle database.
[Reference: Oracle Database Concepts 12c, Data Concurrency and Consistency - Read Consistency, Transactions - Data Manipulation Language, ]
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