Questions for the SQL Interview and Their Answers
SQL is a common way to write code for databases, so many IT professionals may need to know it. This includes programmers, data scientists or analysts, database managers, and others.
This article has sample questions and answers that will help you get ready for your next SQL interview.
What does it stand for?
One of the most common ways to “talk” to a database is through Structured Query Language, or SQL. SQL tells the database what to do by sending it commands. This includes adding data, getting it back, and getting rid of it. Some of the most commonly used SQL commands are select, insert, update, delete, create, drop, and drop.
You can do most things with a database by using these commands. Many enterprise SQL users add features that go beyond SQL and are unique to the organization’s database.
SQL programmers need to be able to write code in more than one language because of this. But SQL is very important for many programmers who work on the backend, which is the part of a company’s website and app infrastructure that users don’t see.
Common SQL interview questions
If you are getting ready for a SQL interview, you should look over some common interview questions, like these SQL interview questions and answers. It’s important to be able to link what you say to what you’ve done during an interview. One way to do this is to answer interview questions using the STAR method.
STAR makes you think about situations, tasks, actions, and responses so you can come up with useful answers.
- Tell me about SQL.
- What does it stand for?
- Define database.
- What’s the difference between a table and a field?
- What are a primary key, a unique key, and a foreign key?
- Can you explain what normalization is and how it works with databases?
- What are the parts of SQL?
- Explain what data integrity is and how it affects your work.
- Write a SQL query that displays the date.
- List and explain the types of joins.
- Explain what things are and how they are related.
Tell me about SQL.
If you’re going for a more general IT job like systems administrator or backend programmer, SQL questions and answers are likely to be a small part of the interview process. You will have to show that you know a lot about other things, like how to use different programming languages and how hardware and software work.
This kind of question could be the first in a series of SQL questions that test how well you know the query language. SQL can be explained in two different ways. First, tell me what the letters stand for. What does SQL do then?
SQL stands for Structured Query Language. It is a standard language for telling the database what to do. It does this with commands like “Select,” “Insert,” “Update,” “Delete,” “Create,” and “Drop,” which cover most of the functions that large businesses need to better use their data.
What does it stand for?
Another basic question wants to know if you know the difference between a database management system (DBMS) and something like a database.
There is a strong link between these two things, but they are also very different. You should also try to show that you know how important SQL is to using a DBMS.
“DBMS stands for Database Management System, which is the system that controls, monitors, and keeps a database up-to-date. A database is just a place to store information on its own. Until you add the DBMS, which lets you control the data life cycle, it doesn’t do much more than that.
Define database
To understand what SQL is for and how to use it, you need to know at least the basics about databases. If you can show that you know these basics well and intelligently, it will set the stage for a more advanced conversation with a potential employer.
Example: “A database is a place to keep information. It’s one of the most basic parts of a company’s data infrastructure. It works with a DBMS to finish simple data-related tasks.”
What’s the difference between a table and a field?
Programming has a lot of fine points. When you are asked to compare two or more things, you can show that you can think critically by giving a multifaceted answer. During a SQL interview, you might be asked about the following differences:
- Delete vs. truncate
- Local vs. global variables
- Cluster vs. non-cluster index, among other things
“Tables and fields are both types of objects. Tables are put together by rows and columns. Columns go up and down, and rows go across and down. Records, which are the rows in a table, can have any number of rows. It has a certain number of columns, also called “fields.” In a nutshell, fields are the columns in a table.”
What do primary, unique, and foreign key mean?
Keys are groups of fields that SQL programmers can use to do their work. They tell what a row is made of. Your answer should go beyond this simple definition by giving a specific example, preferably using the STAR method.
Example: “A unique key is a constraint that mandates a unique identifier for records in a database.
A unique key constraint is part of a primary key constraint. A table can have many unique constraints, but only one primary key constraint. The primary key constraint is a set of fields that tell the database that a row is unique. NULL can never be used to describe it.
A foreign key is a restriction that links the primary key of one table to the primary key of another table.
Using these limits, I was able to make an HR database that had all employee information in it. The record number was the primary key because we used that number to find and sort employee records.
But the employee number column also had to be different. No two numbers could be the same. I used a unique key constraint to make sure that each item in this data set was unique. Because of this, nobody was given the same employee number.”
Can you explain what normalization is and how it works with databases?
Normalization is a term that could come up for anyone who works with databases for a living. Normalization and how it affects databases are things that a SQL programmer or anyone else who works with SQL should know. To answer this question, you should carefully explain what normalization is and what it means for a database.
Normalization is the process of putting data in order using fields and tables to get rid of duplicates, redundancies, and dependencies. Normalization lets you add, change, or remove information from a single table.”
What are the parts of SQL?
This question wants a simple list. You can show how well you know SQL by giving a short explanation for each item on the list. In a SQL interview, you may also be asked to describe the following lists:
- Functions set by the user
- Different kinds of collation sensitivity
- DBMS types, plus
Example: “DDL, or Data Definition Language, lets you do different things with the database. Create, Delete, and Change are some of these.
DCL, or Data Control Language, lets you do things with a database. This is how system administrators give and take away access privileges.
With DML, or Data Manipulation Language, you can change data. This includes insert and update queries.”
Explain what data integrity means and why it’s important for your job.
When building an enterprise business environment that is built around data, data integrity is very important. SQL developers need to know what “data integrity” means and why it’s important so that data can be used. Here, you could give an example of how your role in an organization changed because of how well data was kept.
“Data integrity is the best thing that can happen to corporate data. It is known for having accurate and consistent data, which makes it very useful. It is the goal of maintaining the data lifecycle, which is the process of collecting, processing, and maintaining data.
Write a SQL query that displays the date.
As part of the interview, some people may ask you to write in the SQL language. Before your interview, it’s important to brush up on SQL programming details and how they work in enterprise business. Before the interview, you might want to try writing some code.
“The GETDATE query gets the date for today. GETDATE();”
List and explain the types of joins
Joins may be an important part of what a SQL developer does every day. To show that you know about joins, make a list of them and say a few words about each one.
“Inner join returns rows with at least one match between the two tables.” Right join gives you all the rows on the right side of the table, even if they don’t match the rows on the left side. Left join does the opposite. It gives you rows on the left that don’t match on the right. Full join finds matches in any table, no matter where they are.
Explain things and how they are connected.
When you are asked to explain something complicated, make sure you use words that people will understand. Interviewers may sometimes want to see that you can talk about IT concepts in simple terms. Practice talking about things like entities and relationships as if you were talking to someone who had never heard of them before.
“Entities are any person or thing about which you can store information. This could be information about your bank or your customer relationships. There are many things that could happen. Relationships show how entities are connected in a hierarchical way, and they are often used in the data structure and modeling of entities.
