Adventures in Machine Learning

Boost Your IT Career with Strong SQL Skills

Boosting Your Career with SQLIn today’s rapidly evolving IT landscape, many software applications require extensive data handling capabilities. For data-driven jobs, SQL skills are in high demand, making SQL a valuable tool for anyone looking to advance in their career in the technology industry.

With strong knowledge of SQL, you can enter a vast pool of IT job opportunities. Importance of Learning SQL:

SQL, short for Structured Query Language, is a domain-specific language used in the management of relational databases.

The ability to understand SQL and work with it is an essential skill for anyone involved with data handling, especially in databases. SQL is used in multiple applications; thus, SQL skills are in high demand across diverse industries.

In data-driven jobs, SQL skills are particularly valuable. As data has become ubiquitous in the business world, competence with data analysis and manipulation using SQL is becoming a critical requirement for businesses.

Employers recognise the value of hiring individuals with a strong background in SQL, so many job listings these days list “SQL skills” as an essential requirement. Applications of SQL:

SQL is the most widely used query language on the market, making it a valuable tool for anyone interested in pursuing a career in IT.

SQL is used to manage databases, query data, and create reports. SQL is a standard language, so proficiency in SQL can be applicable across diverse industries.

SQL can be used in numerous industries, including IT, data science, finance, retail, healthcare, and many others. In IT, an individual with strong SQL skills could manage and administer databases.

In data science, SQL is used to clean, transform, and analyse data. In finance, SQL is used to create financial reports and analyse financial trends.

In retail, SQL helps to manage inventory and sales databases. In healthcare, SQL can be used to extract and analyse patient data.

Basic SQL Whiteboard Questions:

During a job interview, basic SQL whiteboard questions are commonly utilised by interviewers to test your proficiency in SQL. These questions may typically involve using the “SELECT” statement to extract data from tables, accompanied by ‘WHERE’, ‘JOIN’, ‘GROUP BY’, or ‘ORDER BY’.

Interviewers often test your ability to use these operators to manipulate tables and create targeted queries. To prepare for your interview, you should familiarise yourself with these whiteboard questions and make sure you know how to solve them.

Practising these questions using sample data sets can help to ensure that you will be adequately prepared to answer SQL questions in any job interview. Practical SQL exercises:

Practical SQL exercises consist of using SQL statements to build, query, and manipulate databases.

These exercises are hands-on and involve working through relevant problems. In practical exercises, common errors, queries containing duplicates, and complex queries are taught.

Among the queries that can be learned are scheduled maintenance activities, data cleaning, and designing analytical reports. Developers who already grasp the theoretical aspects of SQL can use this type of exercise to enhance their practical skills and knowledge of the language.

Expert programmers can take these exercises to test themselves and consolidate their knowledge, while beginners can use these exercises to grasp the fundamental principles of SQL. Practice exercises libraries such as ‘Codingame’, ‘Codecademy’, and ‘SQL Practice Problems’ can help hone your practical skills.


If you want to succeed in a data-driven career, developing your SQL skills is a must. SQL is in high demand in numerous industries, making it a valuable tool for programmers and developers across diverse industries.

By practising practical exercises and mastering whiteboard questions, you can demonstrate your SQL proficiency to potential employers. With SQL skills, you can open up a vast pool of employment opportunities.

Basic SQL Whiteboard Questions for Job Interviews

SQL is a domain-specific language used for relational databases management. It is a standardised language used in diverse industries, including IT, finance, healthcare, retail, education, among others.

Almost all data-driven jobs require basic SQL knowledge, and it is, therefore, essential to master SQL whiteboard questions.

Elements of SQL Query:

An SQL query is a statement used to retrieve, update, add, or delete data from a database.

An SQL query comprises primarily three basic elements, namely; SELECT, FROM, and WHERE. The SELECT clause is used to specify the columns or fields that need to be retrieved from the database.

The FROM clause is used to specify the table or tables that contain the data needed for the query. The WHERE clause is used to specify a condition to filter the rows.

SQL Clauses:

Apart from the primary elements of an SQL query, several clauses are used to manipulate data in the database. The WHERE clause is used to filter rows based on a condition.

The LIKE clause is used to search for a pattern in the data. The NOT LIKE clause is used to exclude rows that match a pattern.

The AND, OR, and NOT operators are used to combine conditions. The HAVING clause is used to filter the data in groups by conditions.

The ORDER BY clause is used to sort the result set in ascending or descending order based on a particular column or columns. SQL Functions and Keywords:

SQL functions and keywords are useful tools in manipulating data and generating reports from the database.

The NULL keyword is used to represent a missing or unknown value in the database. The JOIN keyword is used to combine rows from two or more tables.

The GROUP BY clause is used to group rows with common data. The UNION, UNION ALL, INTERSECT, and MINUS keywords are used to combine results from multiple SELECT statements.

The DISTINCT keyword is used to retrieve the unique records in a dataset. The ALIAS keyword is used to give a table or column a temporary name.

Practical SQL Exercises for Interview:

Practical SQL exercises mimic real-world applications of SQL. The following are practical SQL exercises for interview preparation:

SQL Statements and Queries:

A school has multiple subjects that are taught by different lecturers.

All students must take ten courses to graduate. Write SQL statements that can identify the students who have not completed all ten courses and display their names.

A company has numerous departments, each having a head manager and workers. Write SQL queries to identify departments with more than ten workers and show the names of their managers and the total number of workers in each department.

SQL Errors and Duplicates:

In a school, a student can only belong to one department. However, the student data table has a department column containing duplicates.

Find and eliminate all the rows that contain such errors.

A worker table has duplicate entries for the same person.

Write an SQL query to keep only one record per person. Complex SQL Queries:

In a school, some students have selected multiple courses, and some courses have multiple students.

Write an SQL query that can identify the courses with the maximum and minimum number of students, together with their respective number of students, sorted by the course name.

In a retail company, the sales team gets commissions based on the number of sales they make.

The team with the most sales receives a bonus. Write an SQL query that can identify the teams that should get the bonus.


SQL whiteboard questions test one’s ability to use SQL to manipulate data in a database. The primary elements of an SQL query include the SELECT, FROM, and WHERE clauses.

Other clauses such as WHERE, HAVING, and ORDER BY are used to filter, group, and sort data. SQL functions and keywords such as NULL, JOIN, GROUP BY, Alias, and UNION are also essential tools for manipulating data.

Practical exercises that replicate real-world applications of SQL are among the best preparation strategies for interviews. Finally, complex SQL queries may require multiple SQL statements and advanced SQL knowledge to manipulate data.

Advanced SQL Whiteboard Questions

SQL is a widely used query language for managing relational databases. While basic SQL skills are essential, mastering advanced SQL concepts is necessary to stand out in the job market as a programmer, database administrator, data analyst, or data scientist.

Advanced SQL whiteboard questions may include database management, relational database concepts, and SQL functions and datatypes. Relational Databases:

A relational database is a type of database that organises data into one or more tables.

Relational databases use the primary key and foreign key concepts to manage data relationships between tables. The primary key is a unique identifier of a record in a table, while the foreign key is a reference to the primary key in another table.

Normalization is a technique used to avoid data redundancy in relational database design, while denormalization is the opposite of normalization. Indexing helps to improve the retrieval speed of data from a table.

Database Management:

Database management concepts help database administrators (DBAs) to manage databases effectively and efficiently. A cursor is a database object used to traverse records in a database.

Constraints are rules that ensure data consistency and avoid invalid data in a database. A transaction is a sequence of operations on a database that must complete entirely or otherwise must be aborted.

Locks are a mechanism used to manage database access, preventing multiple transactions from making changes to the same data concurrently. SQL Functions and Datatypes:

SQL functions are built-in functions that perform specific tasks in SQL queries.

Some advanced SQL functions include NULLIF, NVL, RANK(), DENSE_RANK(). The NULLIF function compares the arguments and returns null if they are equal.

The NVL function replaces a null value with an alternative value. The RANK() function assigns a unique rank to each row within a query’s result set.

The DENSE_RANK() function assigns a rank based on unique values within a query’s result set. Datatypes help to determine the type of data stored in a column.

Common datatypes in SQL include VARCHAR2 and CHAR. Conclusion:

Mastering advanced SQL concepts is essential for IT professionals who want to stand out in the job market and become top-performing data analysts, data scientists, programmers, or database administrators.

SQL whiteboard questions involving advanced concepts may cover database management, relational database concepts, and SQL functions and datatypes. With an in-depth understanding of these topics, IT professionals will be better equipped to handle complex SQL scenarios and drive impressive results for their organisations.

In summary, mastering SQL is an essential skill for anyone looking to advance in their career in the technology industry. SQL skills are in high demand, making it a valuable tool for programmers, database administrators, data analysts, and data scientists across diverse industries.

Basic SQL skills are essential, but mastering advanced SQL concepts is necessary to stand out in the job market and become a top-performing data professional. Whether it is basic or advanced SQL whiteboard questions, preparation is key to demonstrating your SQL proficiency to potential employers.

By honing your SQL skills, you can open up a vast pool of employment opportunities and take your career to the next level.

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