SQL Basics
A computer language for managing data in database management systems is called SQL, or Structured Query Language. Because Database Management Systems (DBMS) are used in practically every software application, SQL programming skills are extremely coveted and demanded in the industry. To be considered for a position, candidates must successfully complete an interview during which they will be questioned on a range of SQL interview questions.
The following is a curated set of SQL interview questions and answers that will most likely be asked during the SQL interview. Candidates with 3 years of experience as professionals may be asked basic SQL interview questions all the way up to advanced level SQL interview questions, depending on their level of skill and other factors. The list below includes all of the SQL technical interview questions for new hires as well as SQL server interview questions for seasoned candidates and a few SQL query interview questions.
How to prepare for an SQL interview?
One of the most important aspects of any analytics interview, be it for data or products or business analytics, is the SQL interview. This round is extremely important to big internet companies like Amazon, Uber, and Facebook, to mention a few.
Going through and reviewing all possible SQL question variations may seem onerous if you are prepared for one. Here is a guide with some sample queries and questions that you must practise before attending your next SQL interview in order to aid you in the process. This is what I’ve put up based on my personal experiences sitting on both sides of the table.
Four levels can be used to categorise SQL issues. We will go over each of these levels in this guide along with some typical examples so you can practise (I would suggest without reading the solution).
Level 1: prepare problems using Aggregated functions.
Aggregate functions are SUM(), AVG(), MAX(), MIN(), COUNT().
Level2: coming to the second level prepare problems based on joins and set operations.
Joins: inner join, right join, left join, outer join.
Set operations are: UNION, UNION ALL, EXCEPT, INTERCEPT etc.
Level 3: problems based on windows functions.
Windows function are: RANK(), DENSE_RANK(), LEAD(), LAG() etc.
Level 4: coming to level 4 prepare or practice a combination of all the three levels.
Sample Interview Questions:
What is DBMS?
A database management system (DBMS) is a piece of software that manages the design, maintenance, and use of databases. Data is managed in a database rather than being saved in file systems by a database management system, or DBMS.
What is RDBMS?
Relational Database Management System is referred to as RDBMS. RDBMS organise its data into a set of tables that are connected by shared fields in their columnar data. Additionally, it offers relational operators for modifying the data that is contained in the tables.
What is SQL?
Structured Query Language, or SQL, is the language used to connect with databases. The retrieval, updating, insertion, and deletion of data from a database are all actions that can be carried out using this standard language.
Select is a common SQL command.
What is a Primary Key?
A primary key is a group of fields that identify a row specifically. This unique key type is distinct and has an implied NOT NULL constraint. It indicates that values for primary keys cannot be NULL.
What is a Unique Key?
Each database record was uniquely recognised by a unique key constraint. As a result, the column or group of columns gains uniqueness.
An automatic unique constraint is defined as a primary key constraint. But with Unique Key, this is not the case.
There can be multiple unique constraints declared for each table, but there can only be one primary key constraint.
What is a Foreign Key?
One table that can connect to the main key of another table is said to have a foreign key. It is necessary to link a foreign key to the primary key of another database in order to establish a relationship between two tables.
What is a join?
Join keyword is used to combine two or more tables. This keyword is used to query data from other tables based on how their fields relate to one another. When using JOINs, keys are important.
What is Normalization?
By arranging the fields and tables of a database, the process of normalisation reduces reliance and redundancy. Addition, deletion, and modification of fields that can be made in a single table are the primary goals of normalisation.
What is Denormalization?
Denormalization is a method used to retrieve data from databases with higher to lower normal forms. Additionally, it is the technique of adding redundancy to a table by fusing information from similar tables.
What is a view?
A view is a virtual table made up of only a portion of the data in a table. Views are not virtually present, and storage capacity requirements are reduced. Depending on the relationship, a view may contain data from one or more tables combined.
What is an Index?
An index is a performance improvement technique that enables quicker table record retrieval. A faster way to access data is using an index, which creates an entry for each value.
What is a Stored Procedure?
A function called a stored procedure uses numerous SQL statements to access the database system. A stored procedure compiles many SQL statements and executes them whenever and wherever necessary.
What is delete and truncate?
Rows can be deleted from a table using the DELETE command, and conditional parameters can be specified using the WHERE clause. After a delete statement, you can make a commit or rollback.
TRUNCATE rids the table of all rows. An operation to replicate cannot be revoked which means you cannot be rolled back.
What are ACID Properties??
Atomicity, Consistency, Isolation, and Durability are the four interrelated attributes that make up the acronym ACID. These qualities serve as the foundation for a large portion of any modern relational database system. Grasp many aspects of SQL Server requires an understanding of the ACID attributes of a transaction.
Conclusion
Prepare the basics and the most important topics like joins, set operations, and windows functions. Practice more because practical knowledge gives you the confidence to crack the interview easily. Refer to this free Advanced SQL course if you have an intermediate-level interview.
