Unlock the Power of PL/SQL: Mastering Cognizant’s Interview Questions for Experienced Developers

In the dynamic world of software development, Oracle’s Procedural Language/Structured Query Language (PL/SQL) has emerged as a powerful tool for building robust and scalable applications. As a seasoned developer, mastering PL/SQL is essential for securing a coveted role at Cognizant, a leading global IT services company. In this comprehensive guide, we’ll explore the top PL/SQL interview questions that Cognizant poses to experienced candidates, providing you with the knowledge and strategies to ace your upcoming interview.

Delving into Duplicate Record Management

One of the fundamental tasks in database management is handling duplicate records, and Cognizant is keen to assess your proficiency in this area. Prepare yourself for a question like:

Write a SQL query to delete duplicate records from a table.

To tackle this challenge, you can employ various techniques, such as using subqueries, analytic functions, or temporary tables. Here’s an example using the ROW_NUMBER() analytic function:

WITH cte AS (    SELECT        t.*,        ROW_NUMBER() OVER (PARTITION BY col1, col2, ... ORDER BY col1, col2, ...) rn    FROM        your_table t)DELETE FROM cteWHERE rn > 1;

In this approach, the ROW_NUMBER() function assigns a sequential number to each row within a partition defined by the columns col1, col2, etc. The duplicate rows will have the same row number, allowing you to delete them by keeping only the row with rn = 1.

Parsing Techniques and Cursor Management

Cognizant interviewers may delve into the intricacies of PL/SQL by asking questions related to parsing and cursor management. Be prepared to explain the differences between concepts like:

Difference between soft parsing and hard parsing of SQL.

• Soft Parsing: When the SQL statement is already present in the shared pool, the Oracle database performs a soft parse, which involves finding and re-using the existing statement from the shared pool, saving time and memory.
• Hard Parsing: When the SQL statement is not found in the shared pool, the Oracle database performs a hard parse, which involves parsing the statement, allocating memory, and creating a new execution plan. This process is more resource-intensive and can impact performance.

Difference between implicit and explicit cursors.

• Implicit Cursors: These are automatically created by the Oracle database when executing SQL statements that return result sets, such as SELECT statements. They are temporary and can only be accessed within the scope of the block where they were created.
• Explicit Cursors: These are user-defined cursors that allow you to control the processing of result sets manually. They provide more flexibility and control over the data retrieval process, but require more coding and management.

Diving into Procedural Constructs

Cognizant may also test your understanding of procedural constructs in PL/SQL, such as procedures and functions. Be prepared to discuss:

Difference between a procedure and a function.

• Procedure: A procedure is a reusable block of PL/SQL code that performs a specific task or set of tasks. It can accept input parameters, but it cannot return a value directly.
• Function: A function is similar to a procedure, but it can return a single value. Functions are typically used to perform calculations or transformations on data and can be included in SQL statements.

Exploring Advanced Querying Techniques

As an experienced developer, you should be familiar with advanced querying techniques in PL/SQL. Cognizant interviewers may pose a question like:

Write a SQL query to find the nth highest salary from a table.

To address this challenge, you can leverage analytic functions like DENSE_RANK() or ROW_NUMBER() along with subqueries or common table expressions (CTEs). Here’s an example using a CTE:

WITH cte AS (    SELECT        sal,        DENSE_RANK() OVER (ORDER BY sal DESC) rnk    FROM        employees)SELECT    salFROM    cteWHERE    rnk = n; -- Replace n with the desired rank

This query first creates a CTE that assigns a dense rank to each salary value based on the descending order. Then, the outer query retrieves the salary value corresponding to the desired rank n.

Preparing for Success

In addition to mastering the technical aspects of PL/SQL, it’s crucial to showcase your problem-solving abilities, attention to detail, and effective communication skills during the interview process. Here are some tips to help you prepare:

1. Practice, Practice, Practice: Solve as many PL/SQL coding challenges and practice questions as possible to sharpen your skills and build confidence.

2. Understand Cognizant’s Business Domains: Research Cognizant’s areas of expertise and the types of applications they develop to better understand the context in which your PL/SQL knowledge will be applied.

3. Brush up on Database Concepts: Ensure that you have a solid understanding of database concepts such as normalization, indexing, and optimization techniques, as these topics may be explored during the interview.

4. Prepare for Behavioral Questions: In addition to technical questions, Cognizant interviewers may ask behavioral questions to assess your problem-solving abilities, teamwork skills, and ability to adapt to changing requirements.

5. Stay Updated: Keep yourself informed about the latest trends, best practices, and emerging technologies in the PL/SQL and Oracle database ecosystems.

By combining a deep understanding of PL/SQL concepts, practical experience, and effective preparation strategies, you’ll be well-equipped to tackle Cognizant’s interview questions and showcase your expertise as an experienced PL/SQL developer.

Remember, the interview process is not only an opportunity for Cognizant to evaluate your skills but also a chance for you to demonstrate your passion for software development and your commitment to continuous learning and growth.

Good luck with your Cognizant PL/SQL interview!