PL/SQL Developer Interview Questions

As an Oracle PL/SQL Developer with 5 years of experience at an advanced level and working as a Technical Lead, interview questions would typically focus on your expertise in PL/SQL, advanced techniques, and your experience in handling complex database applications. Below is a summary of common expected interview questions for this role, including the procedures and concepts you may be expected to know:

1. PL/SQL Fundamentals

Question: Can you explain the differences between a procedure and a function in PL/SQL?

Expected Answer:

A procedure does not return a value and is primarily used to perform an action or modify data. It can accept parameters (IN, OUT, IN OUT) to handle dynamic data during execution.

A function returns a value, often used to compute and return a result. A function can be used in SQL expressions or queries directly, whereas a procedure cannot.

Follow-up: How do you handle error management in procedures?

Expected Answer:

Use the EXCEPTION block to capture and handle runtime errors. Common exceptions include NO_DATA_FOUND, TOO_MANY_ROWS, and custom exceptions. You can also use SQLCODE and SQLERRM to get detailed error information.

1. Cursors (Normal vs. Ref Cursors)

Question: What is the difference between normal cursors and ref cursors? How do you manage them in PL/SQL?

Expected Answer:

A normal cursor is static and is declared in the declaration section, holding a query result set. It is most often used when the query structure is predefined.

A ref cursor is a dynamic cursor that can be assigned to a query at runtime. It allows for more flexible and reusable code, especially in applications that need to process variable queries.

For ref cursors, you can use SYS_REFCURSOR to hold and pass the result set between procedures and functions dynamically.

Follow-up: When do you use sys_refcursor in PL/SQL?

Expected Answer:

SYS_REFCURSOR is used in dynamic SQL scenarios where the query itself is not known at compile time. It provides flexibility to handle queries passed from the application dynamically.

1. Triggers

Question: What are database triggers? Can you give an example of when you would use them?

Expected Answer:

A trigger is a PL/SQL block that is automatically executed in response to a specific event on a table or view (INSERT, UPDATE, DELETE).

Example: A trigger might be used to automatically track changes to an employee’s salary or update audit tables after a data modification operation.

BEFORE and AFTER triggers are the most commonly used.

Follow-up: How would you ensure that a trigger performs efficiently, especially when working with large datasets?

Expected Answer:

Minimize the logic inside the trigger. Use bulk operations like FORALL or BULK COLLECT to handle multiple rows of data efficiently. Also, avoid unnecessary complex computations within triggers.

1. Dynamic SQL

Question: What is dynamic SQL in Oracle? How do you use it?

Expected Answer:

Dynamic SQL refers to SQL statements constructed at runtime using the EXECUTE IMMEDIATE statement. It allows for the execution of SQL queries that are built dynamically based on input or program logic.

Example use cases include dynamic filtering, conditional querying, or executing commands based on user input.

It's commonly used in ref cursors or when constructing complex queries that cannot be predefined.

1. Performance Tuning

Question: How do you optimize the performance of PL/SQL code?

Expected Answer:

Identify and address I/O bottlenecks by ensuring that only necessary data is queried (e.g., using proper filtering and indexed columns).

Avoid unnecessary loops in favor of bulk operations like BULK COLLECT and FORALL for processing large data sets.

Use caching mechanisms like PRAGMA AUTONOMOUS_TRANSACTION where appropriate.

Minimize database calls by consolidating logic into fewer procedures or functions.

Use EXPLAIN PLAN to analyze and optimize queries.

Follow-up: Can you explain how EXPLAIN PLAN works?

Expected Answer:

EXPLAIN PLAN shows the execution path Oracle will use to execute a SQL query. It provides details on how the database will access the data (e.g., using indexes, full table scans) and the estimated cost of different query operations.

Analyzing the EXPLAIN PLAN helps to identify performance bottlenecks like full table scans and missing indexes.

1. Packages in PL/SQL

Question: What is an Oracle package and what are its components?

Expected Answer:

A package is a schema object that groups related procedures, functions, variables, and other elements together. It provides a convenient way to organize and manage code.

It consists of two parts:

Package Specification: Declares procedures, functions, types, constants, etc.

Package Body: Contains the actual implementation of the procedures and functions.

Follow-up: When would you use packages? What benefits do they provide?

Expected Answer:

Packages promote modularity, code reusability, and ease of maintenance. They can hide implementation details, and encapsulate logic to make it easier to modify code without impacting dependent applications.

1. Transaction Control

Question: Explain how transaction control works in PL/SQL. How do you handle commits and rollbacks?

Expected Answer:

PL/SQL supports explicit transaction control using COMMIT, ROLLBACK, and SAVEPOINT.

COMMIT is used to save changes made in the transaction to the database, whereas ROLLBACK reverts the changes to the last SAVEPOINT or the start of the transaction.

A SAVEPOINT allows you to mark a point within a transaction so that you can roll back to that specific point without rolling back the entire transaction.

1. Advanced Exception Handling

Question: How would you implement advanced exception handling in PL/SQL?

Expected Answer:

You can create custom exceptions to handle specific errors in your application, using the EXCEPTION block. This ensures that common exceptions are handled in a centralized manner, improving code clarity and robustness.

Use PRAGMA EXCEPTION_INIT to associate error numbers with custom exceptions.

Follow-up: What are user-defined exceptions, and how are they used?

Expected Answer:

User-defined exceptions are custom exceptions declared using DECLARE and raised using RAISE. You can use them to handle specific business logic errors that are not covered by predefined exceptions.

1. Data Security and Privileges

Question: How do you manage data security and user privileges in Oracle?

Expected Answer:

Use GRANT and REVOKE statements to manage user access to tables, views, and other database objects.

Implement roles to group privileges and assign them to users or applications.

For sensitive data, ensure proper encryption and audit trails are in place.

Conclusion:

As an experienced Oracle PL/SQL Developer and Technical Lead, you're expected to have a deep understanding of advanced concepts such as dynamic SQL, performance tuning, transaction control, exception handling, and caching strategies. Your role would involve both coding best practices and ensuring that your team adheres to design patterns and high-quality standards in database development.