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By Vijay Singh Khatri

We live in an era where humans are generating 2.5 quintillion bits of data each day. Data is crucial in business decision-making. The ability to manage data and databases has become a vital part of an organization’s strategy. There are many database Management Systems available, but relational database management is the most popular. This database management system allows users access to and identification of other data within the database. SQL is the heart and soul of relational databases. It is used to access and maintain the database.

Knowing SQL is a prerequisite to becoming a database administrator. SQL is a critical skill that you must have if you want to interview for a job as a database administrator. Let’s get to it. These are the top 13 SQL interview questions.

What’s the Difference between Deleting Statements and Truncate?

It is essential to first understand the delete command before you can do this. To delete a row from a table, you can enter this command. You can also reverse the data with this command. It is also a data manipulation command.

Additionally, you can employ the truncate option to erase all rows from the table. It is impossible to reverse the data. This command is a data definition language and is quicker than the delete command.

If you are asked about the differences between delete and truncate statements, don’t forget that truncate is faster than delete. The truncate comes from the group that defines data, and the delete form is used to manipulate data.

What are Database Management Systems, and how many Types are there?

Let’s say I have to explain database administration software to you. In that case, you’ll need the Database Management System to collect and analyse data from the user’s applications and database.

The information can be retrieved, modified, and deleted. It can also be any data, such as strings, images, etc. One can store nearly every kind of data. There are three types of database management systems: object-oriented, relational, and hierarchical.

These hierarchical database management systems have a style for every kind of relationship. The structure is similar to a tree. The nodes are the records, and the branches are the fields. This type of database management system allows users to access and identify data with other pieces of data. A network database management system supports many members’ records. Object-oriented DBMSs use small, individual applications referred to as objects. Each object contains data and instructions to perform the desired actions.

To describe the database management software for you, you will need the Database Management System to work with the user’s applications and database to collect and analyse the data.

What do you Mean by SQL’s different Subsets?

The various subsets of SQL include:

  • The domain of data definition
  • The language for transaction control
  • The data manipulation language.
  • The data control language.

Data definition language contains the commands that can help you define your database schema. This language allows you to use these commands whenever you need to create a database schema.

The data manipulation language is a collection of commands that allow you to manipulate data in a database. It is also possible to use data manipulation commands to control data in several tables.

The data control language is the language that allows you to control the permissions and other controls for the database systems. If you are an employee of an Enterprise, and they have a database, then obviously, all employees won’t be able to access it. Data control language is mainly about how to give permission to users to access the database.

The language used for transaction control is the final type. These commands handle the transactions that occur within the database. If you need to roll back or perform other types of transactions, you can use the commands from this language.

As I mentioned, there are four main subsets to the sequels. They are known as the Data Definition Language, Data Control Language, Data Manipulation Language, and Construction Control Language.

As I mentioned, there are four main subsets to the sequels. They are known as the Data Definition Language, Data Control Language, Data Manipulation Language, and Construction Control language.

What are Tables and Fields in SQL?

If you have to explain the terms field and table to someone, you’re dealing with databases in SQL, and databases are made up of numerous tables, aren’t they? It’s simple to respond to the question. Tables are collections of data structured in columns and rows, with fields referring to the number of columns in the table. That’s a table you’re looking at. The tables are also given names based on a few columns.

What is the Primary key?

When you work in a database field, you can have many databases with X number of tables. Each table must be linked to the other tables within a database. You must also uniquely identify each column.

The critical element is a set of characteristics that is possible to utilise to identify every Tuple uniquely. If there are three or four candidate Keys in a relationship, it’s possible to choose them as the primary key.

What are Joins in SQL?

This is a frequent question interviewers are asked. A join is used to join rows from several tables with columns that are related. It also is possible to connect two tables or retrieve data. Four significant joins are there in SQL. These are the inner, left, full, and right joins.

What are Constraints?

Constraints can be used to determine the limits of the type of data in the table. When creating a table, you can use constraints to determine the boundary of the data type. And this can be fixed either while creating the table or when ordering the table statement. You can choose one of the two methods.

It is significant to know five primary restrictions:

  • The Not null constraint,
  • The unique constraints
  • The check constraint
  • The default constraint
  • The index constraint

The not null constraints ensure that it is possible to store no null value in the column. And this means that if you mention particular conditions in a specific column of your table, these constraints will ensure that it is not possible to store a null value in that column.

Next, let’s look at the following constraint. This constraint, called unique constraints, ensures that each column has essentially different values. And also to ensure that each row in a column has unique values.

Next, let’s look at the following constraint. The check constraint is a check constraint that ensures all values in a column meet a particular condition. It should use this constraint if you have a specific need.

The default constraint is a collection of default values that are set for a column without any discount. Suppose you have a column with ten rows, and you don’t specify all of the values. In that case, the default constraint will automatically store the default value wherever you don’t determine a value.

We now move on to the final step of constraints. The index constraint is next. One can use it to create and access information from databases quickly.

What are Unique keys?

A unique key is what identifies one row in a table. And this allows for multiple values in a table, including null values. You must ensure that the unique code identifies only one row of the table. Null values and duplicates are both permitted.

What is the Foreign key?

You can use foreign keys to maintain referential integrity by linking data into tables corresponding to the parent table’s foreign key. Friends is the primary key in a parent table. Any activities that might disrupt linkages between the child’s table and the parent table are blocked by a foreign key restriction. If you have a large database with 10 or more tables, you’ll need to use principle keys and important foreign concepts to figure out how the tables are related.

What are the differences between SQL as well as my SQL?

This is a common question because many people are puzzled about the differences between SQL and MySQL. Let me clarify what the differences are. SQL is an English-based language that stands for “structured query language.” MySQL, on the other hand, is a database management programme. SQL is the language that is used to access and administer relational databases. My SQL is relational in nature. Iseman is available across a wide range of platforms. This system, which is supported by a rocker, allows numerous users to access multiple storage engines. These are the key distinctions between SQL and MySQL. SQL is a programming language that is used to connect and manage databases. MySQL is an open-source database management system that is free to use.

What do you Mean by Data Integrity?

Data Integrity is the quality of data as well as the authenticity of the data stored in databases. Integrity also defines business rules that will govern the data’s entry into an application or database. If you are asked this query, you could respond by saying that the integrity of information is the quality and reliability of data.

What do you Mean by Denormalization?

A technique used to switch between the higher and lower forms of a database is called denormalization. It improves the performance of the entire infrastructure by adding redundancy between tables and by incorporating queries from multiple databases into one table.

If you are looking to explain the concept of denormalization, you can say that it’s a sneak. It adds written information into the table by incorporating queries from databases that combine data from different tables. It is possible to use it to access data in higher or lower forms of databases.

What are the differences between Clustered as well as Non-clustered Indexes in SQL?

The clustered index makes it simple to swiftly retrieve all data from databases. It sorts the data in the database by column. A Dom Clustered Index can only be applied to one table. The non-clustered can be used to extract data from a database. The non-clustered index is slower than the Clustered Index, although it is unaffected by storage. In a table, it creates an object that points back to the original table rows.

In addition, a single table could have numerous non-clustered indexes. Both of these can be used to retrieve data more quickly. A clustered index, on the other hand, can only be used by one table. There can be numerous non-clustered tables on a single table.


These are the top 13 interview questions you could ask during interviews. If you have ever written in interviews and were asked questions about SQL, I’m sure you are well aware of question types.

I hope you have read all 13 questions and understood the types of questions you can ask during interviews. If you are preparing for interviews, I wish you all the best.

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