PL/SQL Concepts and Programming Quiz

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Questions and Answers

Give a brief summary on exceptions.

Exceptions are runtime errors that occur during the execution of a program. They can be caused by various factors, such as invalid input, file not found, database connection errors, and more. When an exception occurs, the normal flow of program execution is interrupted, and control is transferred to an exception handler, if one is defined. The exception handler can then take appropriate actions, such as logging the error, displaying an error message to the user, or attempting to recover from the error.

Explain the concept of functions in PL/SQL.

In PL/SQL, functions are subprograms that perform a specific task and return a single value. They are similar to functions in other programming languages. Functions in PL/SQL are designed to encapsulate reusable code blocks, making the code modular and easier to maintain. They can accept input parameters and return a specific data type, such as a number, string, or date.

Write short notes on transaction scope.

A transaction scope in PL/SQL defines the boundary within which a series of database operations are considered as a single unit. It ensures that all operations within the scope are either committed (saved permanently) or rolled back (canceled) together. This concept ensures data consistency and integrity in the database.

Write a PL/SQL program to demonstrate exceptions.

<pre><code class="language-sql">BEGIN -- Attempt to divide by zero DBMS_OUTPUT.PUT_LINE(10 / 0); EXCEPTION WHEN ZERO_DIVIDE THEN DBMS_OUTPUT.PUT_LINE('Error: Division by zero.'); END; / </code></pre> Signup and view all the answers

Give a brief description on associative arrays.

Associative arrays in PL/SQL, also known as indexed-by tables, allow you to associate values with unique keys. Unlike traditional arrays, which use numeric indexes, associative arrays use custom keys to identify and access their elements. This makes them a flexible and powerful data structure for storing and retrieving data based on key-value pairs. Signup and view all the answers

Explain conditional statements in PL/SQL.

Conditional statements in PL/SQL, such as <code>IF-THEN-ELSE</code> and <code>CASE</code> statements, control the flow of program execution based on specific conditions. They allow you to execute different blocks of code depending on whether a particular condition is true or false. This enables you to write logic and make decisions in your PL/SQL code. Signup and view all the answers

How to declare Varray collection type in PL/SQL?

To declare a Varray collection type in PL/SQL, you use the <code>VARRAY</code> keyword followed by a name for the collection and the data type of the elements. For example, you can declare a Varray named 'employee_names' to store a collection of strings like this: <code>TYPE employee_names_array IS VARRAY(10) OF VARCHAR2(50);</code> Signup and view all the answers

Given the table EMPLOYEE (Empno, Name, Salary, Designation, Dept. ID) Write a cursor to select the five highest paid employees from the table.

<pre><code class="language-sql">DECLARE CURSOR high_paid_employees IS SELECT Empno, Name, Salary FROM EMPLOYEE ORDER BY Salary DESC FETCH FIRST 5 ROWS ONLY; emp_record EMPLOYEE%ROWTYPE; BEGIN OPEN high_paid_employees; LOOP FETCH high_paid_employees INTO emp_record; EXIT WHEN high_paid_employees%NOTFOUND; DBMS_OUTPUT.PUT_LINE('Empno: ' || emp_record.Empno || ', Name: ' || emp_record.Name || ', Salary: ' || emp_record.Salary); END LOOP; CLOSE high_paid_employees; END; / </code></pre> Signup and view all the answers

Describe mixed notation and exclusionary notations in PL/SQL.

In PL/SQL, mixed notation and exclusionary notation are used to define SQL statements within PL/SQL blocks. Mixed notation combines SQL statements with PL/SQL elements like variables and control structures, allowing you to manipulate data directly within the SQL statement. Exclusionary notation, on the other hand, involves declaring a separate SQL statement and then using it with PL/SQL elements. This helps to keep the SQL logic distinct from the PL/SQL code. Signup and view all the answers

Differentiate between functions and procedures.

Functions in PL/SQL return a single value, whereas procedures do not return values but can perform operations or modify data. Functions are typically used for calculations, data transformations, or retrieving specific data values. Procedures are often used to handle complex business logic, update data, or manage transactions. Signup and view all the answers

Explain the following. a) Calling subroutines. b) Pass-by-value procedures.

a) Calling subroutines is the process of executing a subprogram (function or procedure) from within your PL/SQL code. You call a subroutine by specifying its name and any necessary parameters. Subroutines help you to break down code into smaller, reusable modules, making the program easier to understand and maintain. b) Pass-by-value procedures are procedures where the values of arguments passed to the procedure are copied to the procedure's local variables. When the procedure executes, changes made to the local variables do not affect the original values of the arguments. This helps to maintain data integrity by preventing accidental modifications to the original variables. Signup and view all the answers

Compare various types of validation methods in PL/SQL.

PL/SQL offers several validation methods to ensure data integrity and prevent invalid data from being entered into the database. Some common methods include: <ul> <li>Data type validation: Checking if the data entered matches the expected data type (e.g., ensuring that a numeric field only receives numbers).</li> <li>Range validation: Verifying that the data falls within a specific range of values (e.g., making sure a number is between 1 and 100).</li> <li>Regular expression validation: Using regular expressions to match data against predefined patterns (e.g., validating email addresses).</li> <li>Custom validation: Creating your own validation rules using PL/SQL code to perform more complex checks based on specific business logic.</li> </ul> Signup and view all the answers

What are definer and invoker rights in database? Explain.

Definer rights and invoker rights are security concepts in databases related to the privileges of executing stored procedures or functions. <ul> <li>Definer rights: Grant access to run the code based on the owner's permissions of the object. This grants access to the user that created the object.</li> <li>Invoker rights: Grant access based on the permissions of the current user running the procedure. This grants access to users that have the right to execute the object, but don't have to own it. This can help ensure that the user running the procedure has the correct privileges to access the data. For example, if a user is allowed to update data in the database, but not delete data, they would be granted <code>UPDATE</code> rights, but not <code>DELETE</code> rights.</li> </ul> Signup and view all the answers

How to manage packages in the database catalog? Explain.

PL/SQL packages provide a structured way to group related procedures, functions, variables, and types. Managing packages in the database catalog involves creating, compiling, and storing them effectively. To manage packages: <ol> <li>Create the package: You use the <code>CREATE PACKAGE</code> statement to define the package structure, including its name, specifications, and body.</li> <li>Compile the package: After creating the package, you should compile it using the <code>CREATE OR REPLACE PACKAGE</code> statement. This ensures that the package's code is properly understood by the database.</li> <li>Store the package: The compiled package is then stored in the database catalog, making it accessible to other PL/SQL programs or users who have the necessary permissions.</li> <li>Maintain the package: As your application evolves, you may need to modify or enhance the package. You can alter or drop the package using the <code>ALTER PACKAGE</code> or <code>DROP PACKAGE</code> statements, respectively.</li> </ol> Signup and view all the answers

Briefly explain system and database event triggers.

Triggers in databases are special procedures that are automatically executed when specific database events occur. <ul> <li>System event triggers: These triggers are associated with events that occur at the system level, such as database startup or shutdown. They can be used for tasks like performance monitoring, data logging, or security auditing.</li> <li>Database event triggers: These triggers are associated with events that affect specific database objects, such as tables, views, or procedures. They can be used to enforce data constraints, audit data changes, or generate notifications when certain events occur.</li> </ul> Signup and view all the answers

Explain the following: a) Database trigger architecture. b) Compound triggers.

a) Database trigger architecture involves defining the trigger's events, timing (before/after), and actions. It specifies when and how the trigger should be executed. The trigger's code includes the logic to perform the desired actions. b) Compound triggers are triggers that consist of two or more trigger blocks. Each block is associated with different events or timings. They allow you to perform complex actions by chaining together multiple trigger blocks to handle different aspects of a particular database event. Signup and view all the answers

Flashcards

Exceptions in PL/SQL

Events that can disrupt the normal flow of execution in a program.

Functions in PL/SQL

Subprograms that return a single value and can be called from SQL.