Software Coders: Here Are 10 SQL Interview Questions and Answers

SQL – or Structured Query Language – is defined by Wikipedia as “a special-purpose programming language designed for managing data held in a relational database management system, or for stream processing in a relational data stream management system.”

In other words, SQL is an invaluable form of software coding – and thousands of jobs requiring the knowledge of and familiarity with SQL are available. Millennials – equipped with their generation-wide technological prowess – have the chance to seize great opportunities in the field.

We’ve already covered questions and answers to get you prepared for your position based in Java programming – but here are ten interview questions and answers gathered from expert sites and blogs to help prepare you for an interview based on your knowledge of SQL. The question topics are carefully selected to vary from definitions to SQL functions to technicalities.

This first set of questions comes recommended by Javapoint.com. We’ll start with the basics.

Question: When did SQL first appear?
Answer: It appeared in 1974.

Question: What are the usages of SQL?
Answer:

To execute queries against a database
To retrieve data from a database
To insert records into a database
To update records in a database
To delete records from a database
To create new databases
To create new tables in a database
To create views in a database

Question: What are the subsets of SQL?
Answer: Data definition language, data manipulation language and data control language.

Now we’ll get down to specific, functional questions. The following two questions – related to the same basic SQL function – were featured on Toptal.com’s page devoted to SQL interviews.

Question: What does “UNION” do?
Answer: “UNION” merges the contents of two structurally compatible tables into a single combined table.

Question: What is the difference between “UNION” and “UNION ALL?”
Answer: “UNION” will omit duplicate records whereas “UNION ALL” will duplicate records.

Our next set of varying basic function questions is provided by tutorialspoint.com.

Question: Is “NULL” value the same as zero or a blank space? If not, why is “NULL” different?
Answer: “NULL” value is not the same as zero or a blank space. It is a value which is ‘unavailable, unassigned, unknown or not applicable’ – whereas zero is a number and a blank space is a character.

Question: What are the purposes of the condition operators “BETWEEN” and “IN?”
Answer: The “BETWEEN” condition operator displays rows based on a range of values. The “IN” condition operator checks for values contained in a specific set of values.

Question: What is the default ordering of data using the “ORDER BY” clause? How could it be changed?
Answer: The default order is ascending. It can be changes by using the “DESC” keyword following the column name in the “ORDER BY” clause.

Finally, here are two “advanced level” SQL questions and answers from biginterview.com’s list.

Question: What is the difference between an inner join and an outer join?
Answer: An inner join involves joining two tables in which a common ID / key exists in both. An outer join is the joining of two tables – but there is no match in the first or second tables.

Question: What port does SQL server run on?
Answer: 1433 is the standard port for SQL server.

While there are multitudes of possibilities for questions based on SQL, you’ll be off to a great start in your interview preparation by studying these questions and answers. Volumes of additional questions are available on any of the websites listed here.