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It is widely used in the programming languages of websites, apps, and other platforms.

What are the basic SQL commands?

Some of the most important SQL Commands are:

What are the four important SQL statements?

SQL databases place a lot of importance on primary keys.

They provide each row in a database table with a unique ID.

What are SQL data types?

User names and passwords are stored in the SQL tables sys.server principals and sys.sql logins, respectively.

Passwords are not stored in normal text.

What is SQL injection?

SQL injection attacks are one of the most common types of cyber-attacks today.

They allow malicious attackers to access data by manipulating an applications database.

The best way to protect against SQL injection attacks is to prevent them from happening in the first place.

What is a trigger in SQL and its types?

Triggers are used to evaluate data before or after data modification using DDL and DML statements.

There are three types of triggers LOGON, DDL, and DML.

How would you distinguish between single-row and multiple-row functions?

A single row in a table can be affected by single row functions at once.

They execute a row and then just give back one result.

It is well known that length and case conversions are single-row functions.

A tables rows can be affected by many row functions simultaneously.

They are also known as group functions, executing multiple rows before returning a single output.

What is Database Normalization, and what are its main four types in SQL?

Database Normalization is a process through which data is organized for faster accessibility and to reduce data redundancy.

Indexes are one of the most important concepts in SQL.

They allow us to quickly find specific rows of data in large databases.

Indexes are used to improve the performance of queries by speeding up the searching of data in tables.

They are also used to improve the readability of data in tables.

Constraints are used to limit the throw in of data that can go into a table.

This ensures the accuracy and reliability of the data in the table.

If there is any violation between the constraint and the data action, the action is aborted.

What are the commonly used SQL constraints?

Commonly used SQL constraints are:

Is NULL equal to 0 in SQL?

A NULL value in SQL denotes a value that is unavailable or assigned.

A space ( ) or zero (0) are not equivalent to the value NULL.

How to prevent SQL injection attacks?

Additionally, quick defenses like a firewall would help to safeguard the SQL database.

What is Dynamic SQL, and when can you use it?

What are the different types of Keys in SQL?

The unique value must be in the primary key.

Primary key fields cannot contain NULL values.

There can be only one primary key per table, consisting of one or more fields.

Tables with primary keys are called parent tables, while tables with foreign keys are called child tables.

Unlike Superkey, all the features of a candidate key must be useful for identifying records.

A composite key is a primary key with some other attribute or column.

What are the types of indexes in SQL?

In SQL, a buffer pool is also referred to as a buffer cache.

A buffer pool can be used by all resources to store their cached data pages.

When setting up a SQL Server instance, the buffer pools size can be specified.

The size of a buffer pool determines how many pages it can hold.

The following are the different types of dependencies in SQL.

Joins are a fundamental part of data management in SQL.

What are the set operators in SQL?

Data from one or more tables of the same punch in can be combined using the set operator.

The SQL set and SQL join operators are similar, but there are some key differences.

SQL set operators collect records from different queries, whereas SQL joins combine columns from different tables.

Compound SQL queries are those that include set operations.

What is DBMS?

In simple terms, a DBMS is a software system that facilitates communication between end-users and a database.

What is RDBMS?

To understand RDBMS, you must first grasp the Relational Databases concept.

Now that the functionality is precise, lets define RDBMS.

An RDBMS is considered a software program that allows users to manage, update, and create relational databases.

Some popular RDBMSs in the market today include MySQL, Microsoft SQL Server, Oracle Database, etc.

What is PostgreSQL?

PostgreSQL is a robust open-source database system that enhances SQL with advanced features for secure and scalable data management.

Discuss the difference between SQL and MySQL.

This makes it more intuitive and versatile for developers.

Below is the tabular form to make it more clear.

Discuss the difference between NoSQL and SQL.

Below is a tabular representation of their differences that might help you gain clarity regarding SQL and NoSQL.

Discuss the difference between SQL and PL/SQL.

SQL and PL/SQL differ in their database manipulation approaches.

PL/SQL includes variables and control structures and can execute multiple operations at once, reducing internet traffic.

SQL is limited to single operations.

PL/SQL offers high-speed data processing, which SQL lacks.

Discuss the differences between OLTP and OLAP.

OLAP is designed for analytical tasks, sourcing historical data from multiple databases and using a data warehouse.

Its slower with large data volumes but doesnt require frequent updates.

In contrast, OLTP is for daily business tasks, managing current operational data with a standard DBMS.

Its faster for essential operations and quick data updates initiated by users.

OLAP is subject-oriented, while OLTP is tool-oriented.

What is the select statement?

The result is stored in a result set, and we can define column headings for clarity.

For example, consider a Products table.

The WHERE clause sets the criteria for selecting only those records where the price is greater than $50.

The result set will include the names and prices of products that meet this condition.

How to use a DISTINCT statement?

SQL DISTINCT is a powerful tool for removing duplicates in query results.

It pairs with SELECT to extract unique values from specific columns or tables.

Key points include:

What is CLAUSE in SQL?

In SQL, youll encounter a range of clauses designed to handle substantial data volumes efficiently.

These clauses act as built-in functions, receiving conditional expressions involving column names or related terms.

Mention some clauses used with select.

Imagine you have a list of numbers: 1, 4, 2, 7, 3.

Youll often see lines connecting them.

These lines represent the types of relations between the tables.

There are three main types of relations:

One-to-Many: This is the most common throw in.

Imagine you have a list of customers, and each customer is associated with a city.

One city can have many customers, but each customer belongs to only one city.

Many-to-Many: This throw in is used when both tables can have multiple entries on both sides.

For example, think about employees making calls to customers.

One employee can call many customers, and one customer can receive calls from many employees.

When you have many on both sides, its a many-to-many relation.

To handle this, you often need a new table in between.

One-to-One: This is rarely used but has its place.

Imagine you want to store employee data and their valid identity cards.

Each employee has only one valid identity card, and each identity card belongs to only one employee.

Its a one-to-one relation.

you might store the identity card details in a separate table and relate them using a foreign key.

Its like figuring out how puzzle pieces fit together to represent your real-world data accurately.

What are Union and Intersect?

UNION: Think of UNION as a way to stack results on top of each other.

It combines data from multiple queries into a single list.

It compares two lists and shows you only the items that appear in both lists.

Example: Imagine you have a list of books your friend read and a list of books you read.

INTERSECT helps you find the books you both read.

These operations are like puzzle pieces, helping you combine or find common elements in your data.

Discuss the difference between cross join and natural join.

How do you remove duplicate rows in SQL?

When working with SQL databases, you may encounter duplicate rows in your tables.

This can happen even if you follow best practices like using primary keys and indexes.

This article will discuss different methods to remove duplicate rows from a SQL table.

Its important to exercise caution when applying these methods to production data.

Always test them in a safe environment before using them on live data.

What are some SQL functions used for manipulating letter cases?

SQL provides several functions that allow you to manipulate letter cases in strings.

What is a UNIQUE Key?

SQLs Unique Key ensures that a tables column has only different values and no repeats.

Its a bit like a Primary Key but allows for one blank value (like empty space).

This can be handy when you want things to be mostly unique but not super strict.

you could also use Unique Keys to connect with other tables.

What is a Foreign Key?

A FOREIGN KEY connects one table to another by referencing the PRIMARY KEY of the second table.

The first table is called the child table, and the second is the parent table.

Its like the child table is borrowing information from the parent table.

What are tokens?

What is BLOB in MYSQL?

This allows you to insert, retrieve, and manage binary data in your database.

Discuss the difference between CHAR and VARCHAR.

Discuss the difference between the BETWEEN and IN condition operators.

In SQL, we have two handy operators: BETWEEN and IN.

They help us compare values in distinct ways.

Its like saying, Is this number between 5 and 10?

On the other hand, the IN operator is like having a checklist.

We use it to see if a value is on our list of accepted values.

For instance, we can ask, Is this name in our list of approved names?

Discuss the difference between IN and EXISTS.

For instance, it helps filter products by CategoryID within a predefined list.

On the other hand, the EXISTS operator checks for row existence returned by a subquery.

Discuss the difference between DROP and TRUNCATE commands.

Here, DROP eliminates the table entirely, while TRUNCATE keeps the table structure but removes its data.

Discuss the difference between the RANK() and DENSE_RANK() functions.

Discuss the difference between COALESCE() & ISNULL().

Key Differences:

Discuss the difference between NVL and NVL2 functions.

In SQL, the NVL() function helps convert a null value into an actual value.

If commission_pct is null, we substitute it with 0.

Another useful function is NVL2(), which evaluates the first expression.

If its not null, it returns the second expression; otherwise, it returns the third expression.

The argument expr1 can have any data throw in.

These functions are handy for dealing with null values and customizing data handling in SQL queries.

Discuss the difference between the WHERE and HAVING clauses.

WHERE filters individual rows based on column values, while HAVING filters grouped results based on aggregate functions.

How do you create empty tables?

To create an empty table in SQL, you’re free to use the CREATE TABLE command.

You specify the tables name and define its columns along with their data types.

However, you dont insert any actual data into the table when creating it.

Its like setting up an empty structure to hold data in the future.

This way, you have a table ready to go, but it starts with no information in it.

Can you explain the steps to create a temporary table?

Which types of tables are commonly used in MySQL, and how do they serve different purposes?

This keyword ensures that only different values are shown for the chosen columns.

What are partitioned tables?

This helps manage large datasets and speeds up queries.

People often do this to organize data by time, numbers, or locations.

Different databases support partitioning, but the details can vary.

How to copy tables in SQL?

The new table inherits some basics but not indexes or auto-increment configs.

How to delete a table in SQL?

How can you delete a database in PostgreSQL?

To delete a database in PostgreSQL, you’ve got the option to use the DROP DATABASE command.

First, connect to your database using your preferred database management tool.

After making the alteration, reconfirm the changes success by checking the columns data pop in once more.

What are Nested Triggers?

Nested triggers in SQL databases are like triggers within triggers.

These nested triggers can make your database actions complex and harder to manage.

What is denormalization?

Denormalization in SQL simplifies database tables by introducing redundancy.

Unlike normalization, which minimizes duplication, denormalization intentionally adds redundancy.

Its done to speed up data retrieval by reducing the need for complex joins.

While it can improve query performance, it may lead to data inconsistencies and increased storage needs.

So, use denormalization judiciously to balance performance and data integrity.

What is a View?

In SQL, a view is like a virtual table created by a query.

Its not a real table with data, but it acts like one when you query the database.

What is a Stored Procedure?

Its like having a handy SQL toolbox!

What is a cursor?

In SQL, a cursor is like a virtual hand for handling data row by row.

It helps you work through a list of data, performing actions on each item individually.

Cursors are useful when you need precise control over data operations.

Cursors offer fine-grained data manipulation.

What is a User-defined function?

In SQL, a User-Defined Function (UDF) is a custom tool you create for specific tasks.

Its like your own mini-program in SQL.

UDFs take input, do something with it, and give you results.

UDFs keep your SQL code neat and reusable.

What are Group Functions?

What are scalar functions?

Scalar functions in SQL are like mini-programs that work on individual pieces of data.

They take one value, do something with it, and give you a result.

What are character manipulation functions?

These functions allow you to manipulate and transform text values within your SQL queries.

How many Aggregate functions are available in SQL?

Aggregate functions in SQL provide insights into the data within a database.

For example, AVG calculates the average value of a column in a database.

These functions offer valuable data summaries and insights when querying databases.

What is a unique constraint?

A unique constraint in SQL ensures that a specific column or group of columns doesnt have any duplicate values.

Its like a rule that says, Each value must be unique.

This is commonly used for things like employee IDs or email addresses to prevent duplicates and maintain data integrity.

What is a subquery?

A subquery in SQL is like a query within a query.

It helps you ask specific questions within a larger question.

This nested query is used to filter or calculate data in a structured way.

What is an SQL server?

An SQL server is a software system that manages and stores databases.

Its like a powerful librarian for data.

SQL servers are designed to handle tasks like storing, retrieving, and organizing information efficiently.

SQL servers are widely used in various industries to manage and secure valuable information.

How to start an SQL Server?

Starting SQL Server depends on your operating system and preferences.

On Windows, you might simply smack the Start button, search for SQL Server, and open it.

How to restore the database in SQL Server?

Restoring a database involves taking data from a backup and applying any logged transactions to it.

Essentially, its the process of turning a backup file back into a usable database.

What is schema in SQL Server?

It helps keep things organized, manage who can access what, and prevent naming conflicts.

Its a way to tidy up and control your database world.

What is Database Black Box Testing?

Database black box testing is like testing a vending machine without knowing how its built inside.

Testers interact with the database without peeking into its inner workings.

Its a way to ensure the database works well from the outside, as a user would expect.

What is Data Integrity?

Data integrity in databases means keeping data accurate, complete, and secure.

It ensures that information is correct, not missing, and consistent across the database.

Reliable data is free from errors and safe from unauthorized changes.

It follows the rules and stays protected.

Maintaining relationships between data is important, too.

Keeping track of data changes is part of data integrity.

Its crucial for making good decisions and building trust.

Problems with data integrity can lead to errors and security issues for organizations.

What is a grant command?

In SQL, the GRANT command is used to give specific privileges or permissions to database users or roles.

What is COMMIT?

In SQL, COMMIT is like saving changes to a database.

It makes them permanent, unlike ROLLBACK, which undoes changes.

Discuss differences between commit and checkpoint.

to get to evaluate key SQL principles, you must also practice SQL query interview questions and keep reading.

To gain hands-on experience by executing SQL queries, check out theseSQL practice platforms.