Top 50 Interview Question on SQL with Answer
By: Sumant Jha
Tags: Interview Questions, Database Administration, Sql Server, Sql, Database

SQL Interview Questions

Here, we will talk about mostly asked Interview Question on SQL with Answer. Now in the era of 2.5 quintillion bytes of data being generated every day plays a crucial role in decision-making for business operation. This quite essentially makes up handle data and databases and gives us the need to use the database management system. With various kinds of database management systems present in the market nowadays. The relational database management system is one of the most popular systems available. Now, this type of database management system uses a structure that allows the users to identify and access data in relation to another piece of data in the database. And SQL is the core of a relational database, which is used for accessing and managing the database. So definitely knowing SQL will open the doors for you to become a database administrator.

So guys if you are preparing for interviews to become a database administrator than SQL is one of the important skills that you need to master in. And with the note of this let’s just get started with the interview question on SQL. So the first question that we have is.

1. What are the different subsets of SQL?

Well, the different subsets of SQL are mainly the Data Definition Language (DDL), Data Manipulation Language (DML), (DCL) Data Control Language, and (TCL) Transaction Control Language.

Now coming to the Data Definition Language. This set of language consists of the commands that can be used to define the database schema. So whenever you want to define the database schema, you can use the commands from this particular language.

Coming to the Data Manipulation Language. The manipulation language consists of all the commands that deal with the manipulation of data presented in the database. So for example, if you have n number of tables and you want to manipulate the data and present in those tables, then you use data manipulation commands.

Coming to the Data Control Language. The data control language includes the commands which deal with the right permissions and other controls of the database systems. So for example, you work for an Enterprise and the Enterprise has a database. Now, obviously all the employees will not have access to the database right. So the data control language mainly deals with how you give the user permissions to access the database.

Now coming to the last type of language that is the Transaction Control Language. This basically includes the commands which mainly deal with the transaction of the database whenever you want to roll back or you want to perform any various kind of transactions, then you use the set of commands from this language, right?

So as I said there are mainly four different subsets of sequels that you should mention that is the data definition language, the data manipulation language, the data control language, and the transaction control language.

Now moving on to our next interview question on SQL.

2. What is the difference between DELETE and TRUNCATE statements?

So I’ll start by explaining to you what is the delete command? Well, the delete command is basically used to delete a row in the table. So you can also roll back data after using the delete statement. And it is a data manipulation command.

Coming to the truncate statement, The truncate statement is basically used to delete all the rows from a table and you can not roll back the data. This is a DDL (Data Definition Language) command and it is faster than the delete command.

So anyone asks you the difference between the delete and the truncate statements don’t forget to mention that you know, the truncate statement is definitely faster than the delete statement. And the truncate statement is from the data definition family and the delete statement is the data manipulation family.

From the right now moving on to our next interview question on SQL.

3. What do you mean by Database Management Systems and what are the different types of it?

So now if I have to define the database management system for you, then a database management system is a software application that interacts with the user’s applications and the database itself to capture and analyze the data. And the data stored in a database can be modified retrieved and deleted and can be of any type like the strings number images etc. So you can basically store any kind of data.

Not different kinds of database management systems are the hierarchical the relational the network and the object-oriented database management systems. The talking about the hierarchical database management systems. This type of database management system has a style of predecessor and successive type of relationship. So it has a structure similar to that of a tree. While in the nodes represent the records and the branches of the tree represent the fields.

Coming to the relational database management system. This type of database management system uses a structure that allows the user to identify and access data in relation to another piece of data in the database. The Network database management system supports many to many relations. Where in multiple member records can be linked and the object-oriented database management systems use a small individual software called objects and each object contain a piece of data and instructions for the actions to be done with the data.

So now moving on to our next interview question on SQL.

4. What do you mean by a table and a field in SQL?

So now the answer to this question is quite simple at a Basically refers to a collection of data in an organized manner in forms of rows and columns. And the field refers to the number of columns in the table. if you have to explain to anybody what table and field mean so basically in SQL, you have a database and the database consists of n number of tables, right? So that is basically a table and the tables have few column names, right? And the column names are basically the feet.

So you can explain with an example as you can see below.

I have an employee details table into which the employee details table is a table and the column names in his particular table are the fields.

Now moving on to our next interview question on SQL.

5. What are joins in SQL?

Now, this is one of the most popular questions that is generally asked in your interview question on SQL. So basically a join clause is used to define to combine rows from two or more tables based on related columns between them. It is used to merge two tables or related data from there and there are mainly four types of joins in SQL. That is Inner Join, the Full Join, the Left Join, and the Right Join.

Now moving on to our next interview question on SQL.

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