Ansæt senior og gennemprøvede PL/SQL-udviklere

Hiring the right PL/SQL developer is critical for companies that rely on Oracle databases to manage their data and build robust applications. Skilled PL/SQL developers can significantly enhance your organization's data-driven capabilities.

This guide will cover everything you need to know to hire a top-tier PL/SQL developer, from understanding the skill set to asking the right interview questions.

About PL/SQL

PL/SQL (Procedural Language/Structured Query Language) is a block-structured language developed by Oracle.

It combines the power of SQL with the flexibility of procedural programming. By writing blocks of code that can include loops, conditions, and exception handling, developers can create complex, efficient, and secure database applications. PL/SQL is widely used for building stored procedures, functions, triggers, and packages, making it an essential tool for managing and manipulating data in Oracle databases.

PL/SQL is a must-have technology for companies that use Oracle databases. Many enterprises use Oracle Database in almost every industry.

Must-have technical skills for PL/SQL Developers

• Database design: Knowledge of relational database concepts, design principles, normalization, and indexing.
• Experience in PL/SQL programming: Writing efficient queries, joins, subqueries, stored procedures, functions, triggers, and packages, as well as exception handling and debugging.
• Oracle database: Deep knowledge of Oracle objects like tables, views, packages, and Oracle data types
• Performance tuning: Understanding execution plans, query optimization, relations, and database index execution.
• Oracle tools: Hands-on experience with at least one of the tools like SQL*Plus, PL/SQL Developer, and TOAD.
• Software design patterns: Be aware of design patterns and implement them to write efficient procedures.

Nice-to-have technical skills for PL/SQL Developers

• Knowledge of version control systems, especially Git.
• Experience with data warehousing and ETL processes.
• Knowledge of Java, C#, PHP, and other programming languages.
• Familiarity with the Oracle product family.

Interview questions and example answers

1. Explain the difference between a stored procedure and a function.

Expected answer: A function always returns a value using the return statement, while a procedure may return one or more values through parameters or may not return at all. Functions can be used in typical SQL statements like SELECT, INSERT, UPDATE, and DELETE, while procedures can't.

2. How do you handle exceptions in PL/SQL?

Expected answer: Use BEGIN...EXCEPTION...WHEN…END blocks to catch exceptions and handle errors. Use RAISE_APPLICATION_ERROR or custom error messages for custom exceptions and better debugging.

3. What is the purpose of a cursor in PL/SQL?

Expected answer: A cursor retrieves data row-by-row from a query's result set. Instead of executing a query simultaneously, it allows us to process individual rows fetched from the result set in a loop one row at a time.

4. How would you optimize a slow-running SQL query in Oracle?

Expected answer: Analyze execution plans using EXPLAIN PLAN or DBMS_XPLAN to find the bottleneck. Avoid redundant or unnecessary data retrieval, rewrite complex joins, use indexes effectively, and use hints or optimizer directives if necessary.

5. Describe the use of triggers in Oracle databases.

Expected answer: Triggers are PL/SQL blocks that automatically execute in response to events like INSERT, UPDATE, or DELETE, enforcing data integrity or auditing. If not used properly, triggers may cause performance issues.

6. What is a package in PL/SQL?

Expected answer: PL/SQL packages are a way to organize and encapsulate related procedures, functions, variables, triggers, and other PL/SQL items into a single item. Packages provide a modular approach to write and maintain the code. It makes it easy to manage large codes. A package is compiled and then stored in the database, which can be shared with many applications.

7. How do you ensure transaction atomicity and consistency in PL/SQL?

Expected answer: We use COMMIT and ROLLBACK statements to manage transaction boundaries, ensuring that all changes either succeed or fail together and maintaining database consistency. Also, in some cases, SAVEPOINT and ROLLBACK TO can be used for partial commit and rollback.

8. Explain the difference between IN, OUT, and IN OUT parameters.

Expected answer: IN parameters are used to pass values to procedures and are read-only. OUT parameters are used to return values from a procedure. “IN OUT” parameters provide both.

9. What is %TYPE and %ROWTYPE in PL/SQL?

Expected answer: The %ROWTYPE attribute designates a record type representing a table row, and the %TYPE attribute designates the type of a referenced scalar object, such as another variable or column. When using these attributes for variable declaration, you don't have to know the exact type of the referenced object.

10. Can you explain SYSDATE, LTRIM, EXEC, DUAL.

Expected answer: SYSDATE: Returns the current date and time. LTRIM: This function would trim all the white spaces on the left part of the string. EXEC: Used to execute stored procedures. DUAL: Selecting from the DUAL table is useful for computing a constant expression with the SELECT statement. DUAL is a table automatically created by Oracle Database along with the data dictionary. It has one column, DUMMY, defined to be VARCHAR2(1), and contains one row with a value X.

Summary

Hiring a skilled PL/SQL developer is essential for companies that rely on Oracle databases to manage their data and build scalable applications.

A strong candidate should deeply understand PL/SQL syntax, database design, and performance tuning, and have experience writing stored procedures, functions, and triggers. Nice-to-have skills like cloud experience or data warehousing knowledge can further enhance a developer’s value.

During the interview, focus on asking technical questions that test foundational knowledge and problem-solving abilities. Following this guide, you’ll be well-equipped to identify and hire a PL/SQL developer who can contribute to your organization’s success.