SQL Query Interview Questions for Experienced Developers

Preparing for SQL Query interview questions for experienced developers will help you land your dream job in any top tech or FAANG company. The SQL database market is expanding and companies like Microsoft, Oracle, IBM, Accenture, etc. hire experienced SQL professionals. They seek candidates who will be valuable assets to their organizations.

To crack the SQL interviews, you must have programming skills and be able to handle large database management systems. The interviewer will ask questions based on coding, your experience in SQL, challenges faced, and possibly ask the basics in SQL to test your fundamental understanding.

SQL Interview Questions For 3 Years Experience

Professionals with 3 years of experience in SQL are exposed to learning the basic concepts, including SQL Injection, data types, and other even more basic operations, like writing queries that will fetch data in a specific range. Below are some common questions that test your knowledge of the basic concepts of SQL queries.

Q1. What is SQL injection?

This is one of the commonly asked SQL Query interview questions for professionals with around 3 years of experience. You must know that SQL injection is a widely used hacking technique by hackers to steal data from databases and tables.

The hacker would add some malicious code to steal your credentials if you go to a website and give in your user credentials, inserted in the form of tables. It is better to keep your credentials secure from SQL injection attacks.

Q2. What are the different types of collation sensitivity?

There are four types of collation sensitivity. They are:

• Case sensitivity: ‘A’ and ‘a’ are treated differently.
• Kana sensitivity: Japanese kana characters Katakana and Hiragana are treated differently.
• Width sensitivity: The same character represented in single-byte (half-width) and double-byte (full-width) are treated differently.
• Accent sensitivity: ‘a’ and ‘á’ are treated differently.

Q3. Write a query to find out the data between range.

If you are performing day-to-day activities, then you need to find out the data between a particular range. To achieve this, you have to use between..and operator or greater than and less than the operator. For instance,

Query 1: Using between..and operator

Select * from employee where salary between 60000 and 80000;

Query 2: Using operators (greater than and less than)

Select * from employee where salary >= 60000 and salary <= 80000.

Q4. What are the various data types used in SQL?

Data types is a specific storage format that is used to store column values. A few common data types in SQL are:

• CHAR (size): Minimum size is ‘1’and Maximum size is ‘2000’
• VARCHAR2(size): Minimum size is ‘1’ and Maximum size is ‘4000’
• LONG: 2GB
• RAW (size): Maximum size is 2000
• BLOB: 4GB
• ROWID: 64 base number system representing the unique address of a row in the table
• BFILE: 4GB
• CLOB: 4GB
• DATE
• NUMBER(P,S): " Precision" can range from 1 to 38 and the “Scale” can range from -84 to 127
• LONG RAW: 2GB

Q5. What is a database schema, and what does it hold?

The database schema is the basic skeleton or structure of the database. It defines how data are organized, stored, and accessed. The schema consists of a table, index, and view – along with stored procedures, functions, and triggers.

Each schema belongs to a certain database user who is essentially the owner of the objects inside this schema and has a right to create, drop any object, or alter them as long as they operate within the boundaries of their schema.

SQL Query Interview Questions For 5 Years Experience

SQL Developers with five years of experience are expected to demonstrate a deeper understanding and concepts around advanced features such as joins, data storage structures, and optimization techniques. SQL query interview questions at this level are a test of your ability to work with more complex queries and larger data sizes in an efficient manner.

Q6. What is the discard file?

The discard file stores reflected records based on when clause conditions within the control file. This condition must be satisfied in the table clause. The file extension of the discard file is .dsc. You must specify the discard file within the control file using the discard file clause.

Q7. What Do You Understand About Database Schema And What Does It Hold?

If you are preparing for Oracle SQL interview questions, you must prepare this one thoroughly. A schema is owned by a database user who can manipulate and create new objects within this schema. It is a collection of database objects and contains DB objects, such as tables, clusters, indexes, views, stored procs, functions, and more.

Q8. Explain Non-Equi Join with an example.

This is one of the most asked SQL Query interview questions for experienced professionals. You should know when two or more tables are joined without equal to (=) condition, then that join is referred to as nonequi join. You can use any operator, such as <>, !=, <, >, and between. For example:

SELECT b.Department_ID, b.Department_name 

FROM Employee a, Department b 

WHERE a.Department_id <> b.Department_ID;

Q9. Where is the MyISAM table stored?

All of the MyISAM tables are stored on disk in three files.

• The “.frm” file stores the table definition.
• The data file has a ‘.MYD’ (MYData) extension.
• The index file has a ‘.MYI’ (MYIndex) extension.

Q10. What is the difference between IN and EXISTS?

The IN operator checks whether a value exists in a list of static values or in a subquery. It is generally better to use for smaller data sets. However, the EXISTS operator checks for rows to exist in a subquery and thus is better suited for larger data sets. EXISTS performs well in complex queries with large tables because it returns TRUE if one row matches.

SQL Query Interview Questions for 10 Years Experience

Advanced questions on database management, architecture, and optimization strategies for large-scale systems would be asked by interviewers targeting professionals with 10 years of experience. 

You're likely to have a comprehensive management of complete database systems with their performance and security by the end of a decade. Questions regarding complex SQL operations, advanced joins, privileges, and schema design are meant to determine your command over SQL as a senior professional.

Q11. What are the restrictions on DML operations on views?

DML (Data Manipulation Language) operations are restricted when a view is based on joins, aggregate functions, or DISTINCT elements using INSERT, UPDATE, and DELETE operations. Also, non-updatable views make it impossible to update directly the underlying tables, unless you create INSTEAD OF triggers. These restrictions maintain data integrity and enforce business rules against derived or summarized data in views.

Q12. What is the GRANT query, and how does it work?

SQL uses the GRANT statement to grant particular privileges on objects in the database such as tables and views to users or roles. For example:

GRANT SELECT, INSERT ON employees TO hr_user;

hr_user is granted the execute ability of SELECT and INSERT operations on employees table. The WITH GRANT OPTION clause can further allow the users to grant the same privileges to others.

Q13. Explain Equi Join with an example.

An Equi Join retrieves data from two or more tables where specific columns match exactly using the equality operator (=). Example:

SELECT a.emp_id, b.dept_name  FROM Employee a, Department b  WHERE a.Department_id = b.Department_ID;

Retrieve all employees along with their corresponding department names in case of Department_id equality in both tables.

Q14. What is database white box testing?

White Box Test for database includes testing the internal structure, logic, and database behavior whenever state change occurs. It will test well-stored procedures, triggers, views, constraints, and data integrity.

This is not the case for black-box testing as it does need schema and queries to know about it. It will help minimize SQL queries to be optimized securely and with better business logic written in.

Q15. What are the types of SQL sandbox environments?

SQL sandbox environments are isolated environments for testing and development without disturbing the system of production. Types include:

• Full Sandbox: This contains a full replica of the production environment, which includes data.
• Partial Sandbox: It contains a part of the data and configuration.
• Developer Sandbox: It is a small, scaled-down version that is used by developers to code and test SQL statements. Teams use such environments for testing without risking the integrity of the production environment.

Sample SQL Query Interview Questions for Practice

Being an experienced SQL developer, you must be able to create databases with efficient structures, write optimized queries, triggers, and views for integration with other applications, and understand issues related to network security and performance. 

Here are a few key practice questions for experienced developers that you must prepare to enhance your tech interview prep.

1. How do you avoid duplicate entries in a query?
2. How to find duplicate records in SQL?
3. What is the case WHEN in SQL?
4. How to delete duplicate rows in SQL?
5. How to change the column data type in SQL?
6. What is the ALIAS command?
7. What are the main differences between #temp tables and @table variables and which one is preferred?
8. What is the difference between IN and EXISTS?
9. What are the different tables present in MySQL?
10. What are BLOB and TEXT in MySQL?
11. What is a nested table, and how does it differ from a normal table?
12. How to find the nth highest salary in SQL?
13. How does the ON DELETE CASCADE option work?
14. How does the CASE WHEN clause work in SQL?
15. How do you merge two tables in Oracle?

Recommended Reading: 50+ SQL Interview Questions and Tips on How to Crack Them

SQL Queries Interview Questions for Professionals With 3 Years Experience

If you have an upcoming tech interview in any FAANG company for the position of an experienced developer in SQL, then you must practice these interview questions on SQL Queries for 3 years experienceexperienced to create a strong impact on the interviewers.

1. How to find the nth highest salary in SQL?
2. If you drop a table, does it also drop related objects like constraints, indexes, columns, default, views and sorted procedures?
3. What are the restrictions of DML operations on views?
4. Explain Equi join with an example.
5. How to fetch alternate records from a table?
6. How will you avoid getting duplicate entries in a query?
7. What does this query say? GRANT privilege_name ON object_name TO {user_name|PUBLIC|role_name} [WITH GRANT OPTION];
8. What does myisamchk do?
9. What is database white box testing?
10. What are the different types of SQL sandbox?

Oracle SQL Query Interview Questions for Experienced Professionals

An Oracle SQL Developer must have a deep understanding of AJAX, AWS, Agile, DHTML, ETL, Ext JS, Git, HTML5, data structures, and data warehouse. In addition to this, you must practice these Oracle SQL Query interview questions for experienced professionals questions mentioned below.

1. What is the difference between commit, rollback, and savepoint?
2. What is the difference between entity, attribute, and tuple?
3. What is the difference between user tables and data dictionary?
4. In what scenario can you modify a column in a table?
5. What is a set unused option?
6. What is the main difference between CHAR and VARCHAR2?
7. Describe the following types of Constraints in brief:
   1. not null
   2. unique key
   3. primary key
   4. foreign key
   5. check key
8. What is the difference between on delete cascade and on delete set null?
9. What is the difference between simple and complex views?
10. Describe your experience working with P/SQL and what were the difficulties you faced while working with PL/SQL? How did you overcome them?
11. What are the different functionalities of a Trigger?
12. What is ref cursor (or) cursor variable (or) dynamic cursor?
13. What are triggering events (or) trigger predicate clauses?
14. Explain what the benefits of PL/SQL Packages are.
15. What is the difference between implicit and explicit cursors?
16. What are privileges and grants?
17. Briefly explain what is Literal? Give an example where it can be used.
18. Name the various constraints used in Oracle.
19. How will you differentiate between VARCHAR & VARCHAR2?
20. What do you mean by a database transaction & what all TCL statements are available in Oracle?
21. What is meant by a deadlock situation?
22. How will you distinguish a global variable from a local variable in PL/SQL?

Coding Based Oracle SQL Query Interview Questions for Experienced Professionals

1. Write a PL/SQL program that raises a user-defined exception on Thursday.
2. Write a PL/SQL program to retrieve the emp table and then display the salary.
3. Write a PL/SQL cursor program that is used to calculate the total salary from the emp table without using the sum() function.
4. Write a PL/SQL cursor program to display all employee names and their salary from the emp table by using % not found attributes.
5. What are the types of ref cursors? Write the syntax for each of them.
6. What is the difference between the trim, and delete collection methods?
7. What is Invalid_number, Value_Error?
8. What is the process for PL/SQL compilation?
9. Write the syntax for how the ON-DELETE-CASCADE statement works.
10. Explain the purpose of %TYPE and %ROWTYPE data types with the example.
11. How can we find out the duplicate values in an Oracle table?
12. How will you write a query to get 5th RANK students from the table STUDENT_REPORT?
13. When do we use the Group By clause in SQL Query? Write the syntax for it.
14. Explain by example, where do we use decode and case statements?
15. How will you merge two tables in Oracle?
16. What is a nested table and how is it different from a normal table?

Also read: Oracle Software Engineer and Developer Salary — All Levels

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FAQs: SQL Query Interview Questions for Experienced Professionals

Q1. How to prepare for the SQL Query interview questions for experienced professionals?

If you are an experienced professional with lots of experience, you can crack any tech interview with basic knowledge of SQL. It will help if you practice the SQL Query interview questions for experienced professionals mentioned above and prepare them thoroughly to ace your upcoming interview. You can watch video tutorials, practice speaking the answers before your known ones, or register for free webinars to build confidence in answering the questions.

Q2. What are the five basic SQL commands?

Though this question is the basic one, interviewers check your fundamental knowledge in SQL no matter how experienced you are. So, you must know that there are five basic SQL commands - Data Definition Language (DDL), Data Manipulation Language (DML), Data Control Language (DCL), Transaction Control Language (TCL), and Data Query Language (DQL).

Q3. What are the skills required to crack an SQL interview?

You can create a strong impression on the interviewer if you know how to structure a database, manage it, author SQL statements and clauses, have a profound knowledge of popular database systems, such as MySQL, know how to analyze SQL data, have work knowledge of PHP, and can create a database with SQL and WAMP.

Q4. What is the average salary of an SQL Developer?

The average salary for a SQL developer is $96,398 per year in the United States and a $5,000 cash bonus per year. The salary varies according to the job location and years of experience. For instance, an SQL developer in New York gets $111,554 per year, which will get $99,450 per year in Austin.

Q5. How to become an Oracle PL/SQL developer?

To become an Oracle PL/SQL developer, you must have a bachelor’s degree in computer science, information technology, or any other related field from an accredited university. You must have an in-depth understanding of SQL and Oracle extensions and must be able to develop your database. If you have experience, you can stand out and gain an advanced position as a developer in Oracle. Moreover, if you have certifications in Oracle Database PL/SQL Developer Certified Professional or a Microsoft certification in SQL, you can get an edge over your competitors in recruitment.

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