SQL, or Structured Query Language, is an eminent database management system language. Businesses use SQL programmes and other organizations to access data and information stored in databases and create and modify existing tables. It was IBM scientists in the 1970s who created SQL. SQL is widely supported, easy to learn, and accessible.
SQL is a tool for managing data in databases, facilitating the timely and precise retrieval of the accurate information required by users. SQL’s simplicity belies the language’s power, though. In truth, SQL can do all three: put data into database tables, update data in existing database tables, and delete data from SQL database tables. Additionally, SQL helps alter the structure of a database by adding, removing, and changing tables and other database objects.
SQL lets you change the data in a database using a command set. SQL INSERT is used to add new data to tables in a database, SQL SELECT is used to get data from tables in a database, and SQL UPDATE alters existing records in a database.
One of the most sought-after skills is SQL expertise, as more and more businesses rely on analytics conducted on massive amounts of data to carry their decisions.
Why Should you Learn About SQL Interview Questions
Those well-versed in SQL will help you gain a new level of insight and analysis into your data, enabling you to make more informed business decisions. You should learn SQL interview questions to develop vital SQL skills. The jobs involving SQL skills pay high salaries. Hence, you can get big, high-profile jobs.
The interview questions will help the aspirants to understand SQL properly and prepare them for their careers. We can find SQL everywhere. SQL is used by virtually every major tech company today. SQL is still widely used for data querying and analysis, even at Fortune 500 businesses like Facebook, Google, and Amazon, which have developed their high-performance database systems. You don’t need to learn to code.
What Type of Questions are Asked in SQL
There are two Types of Questions Asked in SQL
- Basic level questions
- Advance level questions
Beginner-Level SQL Interview Questions
Below are some basic SQL interview questions and answers for freshers.
1. What Does SQL Mean
Ans. SQL refers to the Structured Query Language. It’s the go-to language for relational database management systems and works well with data that has been structured using entities and variables connected through relationships. Connections to databases are made via SQL.
2. What are Some Uses of SQL
Ans. The most common uses of SQL are
- Conducting analytical queries that you have set up
- Subset retrieval from databases for use in analytics and transaction processing
- manipulation of database tables by inserting, modifying, and erasing rows and columns
3. Define Database
Ans. A database is a compiled set of records that can be obtained, updated, and viewed digitally from a server or a local computer. There is a standard method for designing and modelling databases, notwithstanding their potential complexity and size.
4. What is DBMS
Ans. The complete form of DBMS is Database Management System.
5. What Does “RDBMS” Stand for
Ans. “RDBMS” means “Relational Database Management System.”
6. Explain the Concept of Normalization
Ans. Data normalization is a technique for arranging database fields and tables to minimize data repetition and dependencies. The process entails building tables and establishing connections between them following predetermined guidelines. These rules make normalization more adaptable by removing redundant and inconsistent dependencies.
7. What is Denormalization
Ans. Denormalization aims to speed up complex queries that involve joining many tables. Hence it is the polar opposite of normalization. An attempt is made to improve database read performance by adding or grouping redundant copies of data.
8. What is SQL Join
Ans. Join is a SQL statement that combines rows from two or more tables with a standard column. Different kinds of Joins help extract the desired information depending on the table link. Joins can be divided into four categories:
- Inner Fusion
- Left Join
- Right Join
- Full Join
9. What is a Primary key
Ans. Each record in a table is given a primary key as its identifier. NULL values are not allowed, and they must contain unique values. There may be only one primary key per table, and it can be a composite key consisting of any number of fields.
10. Define Unique key
Ans. A unique key can only take the value “null” and never accept a value already used. A unique key’s job is to guarantee that each column and row in a table contains only one value.
11. What are the Different Types of SQL
Ans. The primary SQL dialects are as follows: • Data Definition Language • Data Manipulation Language • Data Control Language • Transaction Control Language (TCL)
12. How do OLTP and OLAP Differ
Ans. OLTP stands for online transaction processing. It is an online database modification system. OLAP stands for online analytical processing, and it is an online database query response system.
13. What is a Foreign key
Ans. A foreign key relates to the primary key of another table stored in another database. The primary purpose of a foreign key is to connect two separate tables.
14. What is the Purpose of the FLOOR Function in SQL Server
Ans. The FLOOR() function makes finding the most significant integer value equal to or less than a given number is made more accessible by the FLOOR() function.
15. Can you Explain the UNION, MINUS, and INTERSECT Commands
Ans. The UNION operator combines the data from two tables and eliminates any occurrences of a row that appears more than once in either table.
Rows from the first query are returned, while those from the second are omitted using the MINUS operator.
INTERSECT is used to merge the rows returned by the two queries into a single one.
16. How to Insert a Date in SQL
Ans. Here’s how to enter a date into an MYSQL database
“INSERT INTO tablename (col name, col date) VALUES (‘DATE: Manual Date’, ‘2022-9-10’)”;
17. How can I View Tables in SQL
Ans. The following SQL statement will display the specified table
18. Can you Tell me the Cartesian Product of the Table
Ans. The result of a Cross Join is a Cartesian product.
19. How do I Install SQL Server
Ans. A relational database management system is required to work with SQL queries. It comes in wide varieties, the most popular being ORACLE, MYSQL, and SQL Server. Therefore, we need to set up a Relational Database Management System to use SQL queries.
20. Define Schema in SQL Server
Ans. A database’s schema is an understandable diagram of its internal structure. It creates and defines the connections between the many entities in the database. It alludes to the various restrictions that might be put on a database. In addition, it explains the different data formats. Tables and Views are also supported. The sizes and forms that schemas take are not all the same. Two of the most common are the star schema and the snowflake schema.
21. Explain Constraints
Ans. In SQL, constraints are helpful to set a maximum value for a column of a specific data type. You can select a parameter while making or editing the table statement. The constraints include NOT NULL, CHECK, DEFAULT, UNIQUE, PRIMARY KEY, and FOREIGN KEY.
22. Define “Data Integrity”
Ans. Data integrity describes how precise and consistent a database’s information is. Integrity constraints are also defined to ensure that data entered into an application or database adheres to predefined business rules.
23. Write a SQL Query to Show the Current Date
Ans. SQL includes a built-in method called GetDate() that is useful for retrieving the current date and time.
24. What is an Index, and Name the Different Index Types in SQL
Ans. A faster way to retrieve data from a table is by creating an index. Since an index makes a separate entry for each value, looking things up is much quicker. In SQL, you can use one of three different kinds of indexes
- Union index
- Clustered index
- Non-clustered index
25. In SQL, What Does the Term “Trigger” Refer to
Ans. In SQL, triggers are a subset of stored procedures that can be programmed to run immediately or after specific changes have been made to the data. You can have some code run whenever a particular type of query is run against a table, whether it’s an insert, update, or delete.
26. Can you List the Various SQL Operators
Ans. In SQL, you can utilize any one of three operators
- Number Systems and Arithmetic Operators
- Logical Operators
- Comparison Operators
27. In Comparison to Natural Join, What is the Function of Cross-Join
Ans. The natural join depends on the fact that all columns in both databases share the same name and data type, while the cross join creates the cross product or Cartesian product of the two tables.
28. What Does ETL Stand for in SQL
Ans. Extract, Transform, and Load (ETL)
29. How do I Remove SQL Server
Ans. In Windows 10, you can access the SQL Server by selecting it from the START menu. Simply right-click the icon, and choose “Uninstall” to remove the programme.
30. What is COMMIT
Ans. When the COMMIT command is invoked in a transaction, the changes performed during that transaction are permanently saved to the database.
Advanced-Level SQL Interview Questions
Below are some advanced-level SQL interview questions for experienced.
1. How to Change the SQL Server Password
Ans. Get started with SQL Server Management Studio. To modify the password for a specific database connection, select it from the list. When prompted, select Security from the list of options that appears. You can access your database by clicking the Logins tab. Type your new password twice to confirm the change and click “OK.”
2. What are the key Distinctions Between SQL and PL/SQL
Ans. SQL is a database-structured query language. DML and DDL operations can be carried out with a single query. It is a data-oriented and declarative language. Its primary function is to process information. It allows you to communicate with the server where your database lives. No PL/SQL scripts are permitted.
PL/SQL is a SQL-based database programming language. It is a group of instructions to define an entire process or function. Moreover, the language focuses on applications and procedures. As such, it serves as a tool for programmers. There is no support for communicating with the server hosting the database. As a SQL extension, it can utilize SQL.
3. Why do we use AUTO-INCREMENT
Ans. When a new record is given into a table, AUTO-INCREMENT can be used to produce a unique number automatically. When a new record is entered, the primary key is automatically incremented by one. Hence it is convenient to set it as an AUTO-INCREMENT field. When a new record is added, the AUTO-INCREMENT field’s value increases by 1.
4. What kinds of Third-Party Tools Does SQL Server use
Ans. The SQL Server community relies on the following suite of complementary programmes
- SQL CHECK
- SQL DOC 2
- SQL Backup 5
- SQL Prompt
- Litespeed 5.0
5. What are Magic Tables in SQL Server
Ans. In SQL Server, a “magic table” is a temporary logical table used for inserts, deletions, and updates (DML). Magic tables automatically record the most recent row operations.
6. What is the Distinction Between TRUNCATE and DROP Statements
Ans. TRUNCATE permanently deletes all rows from a table. The DROP command permanently deletes a table from the database.
7. What are Scalar Functions in SQL
Ans. A scalar function takes in several values and outputs a single value that is a function of the inputs. Scalar Functions are as follows:
- UCASE() changes the case of the field you give it.
- LCASE() changes the field to all lowercase letters.
- MID() takes characters from the text field and gives them back.
- FORMAT() sets the structure of the display.
- LEN() tells you how long the text field is.
- ROUND() converts the value of a decimal field to a number.
8. How can we Update the View
Ans. The view can be updated using the SQL CREATE or REPLACE statements.
9. What is SQL Injection
Ans. SQL Injection is a method of attacking databases by inserting malicious SQL statements into an entry field of the database so that the database becomes vulnerable to the attack once the statement is executed. This method is typically employed in attacks against data-driven systems to access private information and perform database administration activities.
10. What is SQL Sandbox
Ans. SQL Sandbox is an isolated area of the SQL server where untrusted code can run without harming the central database.
11. How do I Insert a Record Into a Table, and What is the Proper Syntax
Ans. To add a record to a table, INSERT syntax is used. For example,
INSERT into table name VALUES (value1, value2..);
12. How do you add a Column to a Table
Ans. The following command will add a new column to the table:
ALTER TABLE table name ADD (column name);
13. State the Difference Between Rename and Alias
Ans. The difference between renaming a table or column and using an alias is that the former makes the change permanent, while the latter only affects the name for the time being.
14. Can you List the Various SQL Views
Ans. There are four distinct kinds of views in SQL. These are:
- A simple view is a view that just uses one table and does not use any advanced capabilities, such as the GROUP BY clause.
- Complex View comprises several tables and has a GROUP BY clause and functions.
- An inline view is constructed using a subquery in the FROM clause can simplify a complex query by creating a temporary table.
- Materialized View saves both the definition and the details. It creates copies of data by keeping multiple documents in a safe location.
15. Describe Hybrid OLAP
Ans. Hybrid online analytical processing (HOLAP) stores data in both multidimensional data structures and relational database tables. A relational database houses all the data.
16. Write Down Every kind of User-Defined Function
Ans. There are three different kinds of user-defined functions, which are:
- Scalar Functions
- Inline Table-valued functions
- Multi-statement valued functions
17. What are Local Variables and Global Variables
Ans. Local variables open only inside the function. Nothing else in the code uses these variables or refers to them.
Global variables are applicable anywhere in the programme. The creation of global variables is forbidden in this function.
18. What Does LIKE Mean in SQL
Ans. The LIKE operator determines if the value of an attribute matches a specified string. Here is one example of a LIKE operator:
SELECT * FROM employees WHERE the first name like ‘Steven’;
19. What is ISAM
Ans. ISAM stands for Indexed Sequential Access Method. IBM created it to let people archive and recover information from tapes and other forms of secondary storage.
20. What is Database White box Testing
Ans. Database triggers and logical views, Decision Coverage, Condition Coverage, Statement Coverage, Database Tables, Data models, Database Schema Referential integrity rules, and ACID features are all part of white box testing.
21. In SQL, What is a Cursor
Ans. SQL cursors help to store data from a database temporarily. The cursor can be one of two varieties:
- Implicit cursors: They are system-generated default cursors. A user cannot make an implicit cursor.
- Explicit Cursor: Explicit cursors are user-defined cursors.
22. State the Difference Between CHAR and VARCHAR2 Datatype in SQL
Ans. The CHAR data type helps to store strings of fixed length, while the VARCHAR2 data type helps to keep lines of varying sizes.
23. How can I Sort a Column Using an Alias for the Column
Ans. Instead of using the where clause, you can sort using the column alias in the ORDER BY clause.
24. State the Difference Between COALESCE() & ISNULL()
Ans. COALESCE() accepts two or more parameters, one can apply two or as many parameters, but it returns only the first non-NULL parameter. ISNULL() accepts only 2 parameters.
The first parameter is checked for a NULL value; if it is NULL, the 2nd parameter is returned. Otherwise, it returns the first parameter.
25. Explain Lock Escalation
Ans. When a query is run, it acquires a minor row lock, the smallest available. Locks are promoted to a range or page locks when they encompass too many rows. A table lock could occur if too many pages are closed.
26. Where Should I put Videos in my SQL Server Database
Ans. Videos can be stored by using the FILESTREAM datatype.
27. Enumerate the ACID Properties that Guarantee the Database Transactions are Executed
Ans. Database transactions are guaranteed to be executed in an ACID (Atomicity, Consistency, Isolation, Durability) fashion.
28. Can we Deactivate a Trigger? and if so, how
Ans. We can use “DISABLE TRIGGER triggerName ON” to turn off just one trigger in the database or “DISABLE Trigger ALL ON ALL SERVER” to turn off all triggers.
29. Explain Nested Triggers
Ans. Using INSERT, UPDATE, and DELETE statements, triggers can implement data modification logic; triggers containing data modification logic and other data modification triggers are known as Nested Triggers.
30. What are the Various Subquery Options
Ans. Subqueries can be classified as either correlated or uncorrelated.
- A correlated subquery is a type of subquery that selects data from a table that is referenced in the main query. This type of subquery is not considered an independent query because it refers to another table and a column in a table.
- Non-Correlated subquery is an independent query in which the results of the subquery are substituted in the results of the main query.
Structured query language (SQL) is a crucial part of the database infrastructure. You will have a far better chance of succeeding in the interview for the relevant position if you have a solid grasp of database and SQL concepts.
Even if you have a firm grasp of the fundamental ideas, there are always a few details you are missing that could derail your performance in the interview. I hope this article helps you find answers to the most common SQL interview questions.