To answer this question, you need to understand the concept of locking levels in Oracle database.

Locking levels determine the granularity at which transactions can lock resources (such as tables, rows, or objects) to ensure data consistency and concurrency control.

Let's go through each option to determine which ones are valid locking levels:

Option A) Object level - This option is correct. Object-level locking allows transactions to lock entire database objects, such as tables or views. Transactions can lock an entire object to ensure exclusive access and prevent other transactions from modifying the object.

Option B) Row level - This option is correct. Row-level locking allows transactions to lock individual rows within a table. This locking level provides more granular control and allows multiple transactions to access different rows concurrently.

Option C) Block level - This option is incorrect. Block-level locking is not a valid locking level in Oracle database. Oracle uses multi-versioning to manage concurrency control, which means that transactions can read consistent versions of data without blocking other transactions.

Option D) Schema level - This option is incorrect. Schema-level locking is not a valid locking level in Oracle database. Locking is typically done at a more granular level, such as object or row level, to minimize contention and allow better concurrency control.

Option E) Database level - This option is incorrect. Database-level locking is not a valid locking level in Oracle database. Locking is performed at a more granular level, such as object or row level, to allow concurrent access to different parts of the database.

The correct answers are Option A (Object level) and Option B (Row level). These locking levels are used by transactions in Oracle database to ensure data consistency and concurrency control.

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• Wrong explanation

To answer this question, let's break down the given code:

my @a = ([1, 2, 3, 4], [5, 6, 7, 8]);
print join(' ', @{$a[1]}[1..3]);

In the first line, an array @a is declared and initialized with two array references: [1, 2, 3, 4] and [5, 6, 7, 8].

In the second line, the print statement is used to output the result. The join function is used to concatenate the elements of an array with a specified delimiter. In this case, the delimiter is a space ' '.

The expression @{$a[1]}[1..3] is used to access the elements from the second array reference ($a[1]) using array dereferencing (@{}) and array slicing ([1..3]). This means we are accessing elements 1, 2, and 3 from the second array.

Therefore, the output of the print statement will be 6 7 8, which corresponds to option D: "6 7 8".

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• Wrong explanation