Top 250 SQL Interview Questions and Answers

Yes, I can create 2 tables in SQL and perform operations like INSERT, SELECT, UPDATE, and DELETE.

• Create Table 1: CREATE TABLE employees (id INT, name VARCHAR(50), salary DECIMAL(10,2));

• Create Table 2: CREATE TABLE departments (dept_id INT, dept_name ...read more

Truncate is a DDL operation that removes all records from a table, while Delete is a DML operation that removes specific records.

• Truncate is faster than Delete as it does not log individual row deletions.

• Truncate resets identity columns, while Delete...read more

A pivot table is a data summarization tool used in spreadsheet programs to organize and analyze large amounts of data.

• Pivot tables allow users to quickly summarize and analyze data from different perspectives.

• They can be used to group and aggregate d...read more

SP3 architecture is a security architecture designed to protect against malware attacks.

• SP3 stands for Security Platform 3

• It is a hardware-based security architecture

• It is designed to protect against malware attacks by isolating critical system compo...read more

DML stands for Data Manipulation Language.

• DML is a subset of SQL (Structured Query Language) used to manipulate data in a database.

• It includes commands like INSERT, UPDATE, DELETE, and SELECT.

• DML statements are used to add, modify, or delete data in ...read more

SQL is a language used to manage relational databases, while PL/SQL is a procedural language used to enhance SQL functionality.

• SQL is used to create, modify, and query databases

• PL/SQL is used to create stored procedures, functions, and triggers

• SQL is...read more

SQL join statements are used to combine rows from two or more tables based on a related column between them.

• Join statements are used to retrieve data from multiple tables in a single query.

• Common types of join statements include INNER JOIN, LEFT JOIN...read more

Join two tables on a key column using SQL

• Use the JOIN keyword followed by the name of the second table

• Specify the key column in both tables using the ON keyword

• Choose the type of join (INNER, LEFT, RIGHT, FULL) based on your requirement

To remove duplicates from a table, use the DISTINCT keyword in a SELECT statement.

• Identify the columns that contain duplicates.

• Use the DISTINCT keyword in a SELECT statement to retrieve only unique values.

• Create a new table with the unique values or ...read more

Identifying type of join for given outputs of two tables.

• Inner join: returns only the matching rows from both tables.

• Left join: returns all rows from left table and matching rows from right table.

• Right join: returns all rows from right table and matc...read more

System tables store metadata about the database system while transactional tables store data related to transactions.

• System tables contain information about the database schema, users, permissions, and other system-related data.

• Transactional tables s...read more

Measures are calculations based on aggregated data, while columns are static data columns.

• Measures are dynamic and change based on filters and slicers

• Columns are static and do not change based on filters and slicers

• Measures are used for calculations ...read more

It means that the table or view does not exist in the database.

• The query will fail and return an error message.

• The application may crash or behave unexpectedly.

• The table or view may have been deleted or renamed.

• Check the spelling and syntax of the qu...read more

DBMS stands for Database Management System. SQL is a programming language used to manage and manipulate data in a DBMS.

• DBMS is a software system that allows users to create, manage, and manipulate databases.

• SQL is used to communicate with a DBMS and ...read more

I have extensive experience in performance optimization in SQL.

• Identifying and optimizing slow queries

• Creating and maintaining appropriate indexes

• Using query execution plans to identify bottlenecks

• Optimizing database schema and table design

• Using appr...read more

List of SQL languages

• MySQL

• Oracle

• PostgreSQL

• Microsoft SQL Server

• SQLite

SQL replication is the process of copying data from one database to another. There are three types of SQL replication: snapshot, transactional, and merge.

• Snapshot replication copies a snapshot of the entire database at a specific point in time.

• Transa...read more

Constraints are rules that are enforced on the data in a table.

• Constraints ensure data integrity and consistency.

• They can be used to enforce rules such as uniqueness, primary key, foreign key, etc.

• Constraints can be added to a table during creation o...read more

Window function in SQL is used to perform calculations across a set of table rows related to the current row.

• Window functions are applied to a set of rows related to the current row, known as a window frame.

• They can be used to calculate running total...read more

ORM (Object-Relational Mapping) is a programming technique for converting data between incompatible type systems in SQL databases.

• ORM allows developers to interact with a database using object-oriented programming languages.

• It abstracts the database ...read more

Subqueries in SQL are queries nested within another query. They can be used to retrieve data for further analysis or filtering.

• Subqueries are enclosed within parentheses and can be used in SELECT, FROM, WHERE, and HAVING clauses.

• They can be used to r...read more

The 'exists' operator is used to check for the existence of a field in a document, while the 'in' operator is used to match a field against a list of values.

• The 'exists' operator is used in MongoDB to check if a field exists in a document.

• The 'in' op...read more

Table partitions are a way to divide a large table into smaller, more manageable parts.

• Table partitions help improve query performance by allowing data to be stored and accessed more efficiently.

• Partitions can be based on a range of values (e.g. date...read more

Delete command is used to remove specific rows from a table, while truncate command is used to remove all rows from a table.

• Delete command is a DML (Data Manipulation Language) statement.

• Delete command can be used with a WHERE clause to specify the r...read more

Union and intersection are set operations used in mathematics and computer science.

• Union combines two sets and removes duplicates

• Intersection returns the common elements between two sets

• Example of union: {1,2,3} union {3,4,5} = {1,2,3,4,5}

• Example of ...read more

DDL stands for Data Definition Language and is used to create, modify, and delete database objects in SQL.

• DDL commands include CREATE, ALTER, and DROP.

• CREATE is used to create a new database object like a table or index.

• ALTER is used to modify an exi...read more

To connect to a SQL server using Python, you can use the pyodbc library.

• Install pyodbc library using pip

• Import pyodbc module in your Python script

• Establish a connection using the pyodbc.connect() method, providing the necessary connection details

• Crea...read more