SQL Interview Questions and Answers

Nowadays, the databases are of great importance and most of the companies are keeping their database in a very secure way. If you want to do your career job in the database then you must know a lot of basic things and you should prepare for the basic questions that could be asked at the time of the interview from the employer side. It's quite simple if any interviewer considering you for the profile of database work then definitely they will check the basic knowledge about database handling in you. And they will focus on your technical skills for SQL.  So you should do look at some basic questions and its answers very closely because in your SQL database career job you will perform the activity with database records.

Here we are going to discuss the SQL that communicates with the database. First, we will put some insight into this technical term and try to focus the concept of it, as the database is the basic thing that is required in every field to collect the data and maintain the records, controlled data for easy entrée. We have so many types of databases used to manage data of any management. SQL databases are a very important type of database. In this, we can store a number of records and we can find any record from the various databases as well as delete the record from the database. The same thing is done in the data definition language. This is also known as a structured form of data that can be accessed in so multiple ways. For example, if there is an Employee department then its database would be with the name as Employee database management systems.

Also, we are going to discuss SQL interview questions and answers for developers. Here some complex SQL interview questions are also included because in the interview any type of questions can be asked. The following questions will help you in the interview.

1. Tell us about DBMS?

You should give the answer as – It means a database management system that is used to manage, keep and use databases. And the DBMS does not save any data in files, it manages the only database.

2. Tell us about RDBMS?

You should always try to make your answer and it should be very simple like – It means a relational database management system. RDBMS is the relation between the stored data in the collection of tables and columns of the tables. It provides relational operators.

3. Brief about SQL (structured query language)?

Answer - SQL is a structured query language, which is communicated with the database. This language is used to keep the database update, preserve, delete, retrieve the data from a large database. It also executes queries against databases as well as to get the data from a database. For the insert, delete updates, query implementation records from the database. To create new databases and views in a database you should perform query operations on the database we use SQL.

4. Tell me the tables and Fields in the SQL (structured query language)?

Answer – In the table there are many rows and columns are available and the table is a set of columns and rows and managing the data with the help of the set of data comes into the model. Columns are fixed vertical format while rows are built-in horizontal format. A table has an individual number of columns that interpret the name as fields and rows called records.

5. Tell us about the primary key to SQL?

Answer – In SQL basically keys have their own identity so here a primary key uniquely specifies a row, it is a combination of field and the primary key is a special kind of unique key and the importance of the primary key is not null.

6. What is a unique key to SQL?

Answer - It is the second type of key that is uniquely identified uniquely identifies each record in the database. This provides uniqueness for the set of columns. The primary key is single. Here the data are completely unique records.

7. What is a foreign key?

Answer - Its third type of key called a foreign key of one table can be a primary key of another table. It is a relation between two tables. You should remember the one foreign key table is the primary key table.

8. What is a join in SQL and explain their types?

It’s the somewhere advanced question of SQL so here you should give an answer on as – The Join is a keyword used to perform query data from multiple tables based on their relationship between the fields of the tables. This key plays a major role when you perform when JOINs are used. There are so many types of joins that are used to get back the data from database tables. Here you may perform the Join query on the database as with different way -

a) Inner Join

(b) Right Join

(c) Left Join

(d) Full Join

9. Brief us about normalization in the SQL (structured query language)?

Answer – You should tell the main reason for normalization is to perform all operations in one table like add, delete, modify, etc records with the table. It also minimizes the redundancy and dependency by organizing tables with organizing database records.

10. Brief us about denormalization?

Answer - It helps to get the data access from higher to lower normal forms of the database. Denormalization tells the redundancy into a table by incorporating the data from the associated tables.

11. What are the different types of normalizations?

Answer - In the above first you should take the view of normalization and the types of normalization are follows,

• 1NF – It is the first normal form. This helps to remove all duplicate columns from the table.
• 2NF – It’s a second normal form. Which are placing a subset of data in separate tables and the creative relationships between the tables using primary keys? It meets all requirements of the 1st type of NF.
• 3NF – It’s a third normal form. It meets all requirements of the 2nd type of NF. This normal form removes the columns which are not dependent on primary key constraints.
• 4NF - It’s a fourth normal form. It meets all the requirements of the 3rd type of NF. It also has multi-valued dependency is not there in 4th NF.

12. What is a View in SQL?

Answer – It is also similar to trigger the View is a virtual table consisting of a subset of data contained in a table. The views are not virtually present and it takes less space in the table. Views have a combination of data one or more tables. It depends on the interview.

13. What is an Index in SQL and explain the different types of indexes?

Answer - To get data very fast in SQL it uses the index, so that faster retrieving of records from the table gets done.

There are the types of indexes as follows,

a) Unique Index Type – It does not have duplicate values it has a unique value. When the primary key is defined,  a unique key automatically works.

b) Clustered Index Type – In every table has its one clustered table. It searches the records with the help of key values records.

c) NonClustered Index Type – It always helps to maintain the logical order of the data. Every table has so many nonclustered indexes.

15. What is a Cursor in SQL (structured query language)?

Answer - It is the same as a pointer that works like a cursor. The cursor is very much useful for traversing the data from the database table.

16. What are the types of relationships and what are they?

You should answer - the connection between the table and database are known as database relationships.

The types of relationships are as

a) One to One Relationship

b) One to Many Relationships

c) Many to One Relationship

d) Self-Referencing Relationship.

17. What is a query in SQL (structured query language)?

It is a simple question of the database and you should answer it confidently - we use the query in the database to get the information from the database. And the query can be matched with our past of the result set.

18. What is the subquery and explain their types?

Answer – You can write the query in that is a subquery, in that inner query and subquery while the outer query called as outer query. Subquery executes first and the outer query can solve after subquery and a combination of both queries is the final answer of the query.

There are types of subquery as,

a) Correlated subquery – The associated subquery is a dependent query, but it can refer to the column in a table.

b)Non-correlated sub query – Here the subquery can be considered as an independent query.

19. What does trigger in SQL?

Answer - A database trigger is one type of program with the help of records response will come when some event on a table is done. A trigger helps to maintain the integrity of the database.

20. What is DELETE and TRUNCATE query in structured query language?

Answer - DELETE query is used to remove rows from the table, and but the specific record can delete in this type of query by using where clause. A TRUNCATE query can remove all rows from the table of the database.

 21. What are the local and global variables in SQL?

Answer – Local variables are a part of the database. These variables are used within the functions. And the global variables can be used throughout the program of code when the function is called that time global variable is not formed.

22. What are user-defined functions in SQL?

Answer - The function has its own identity and its use to get the data with the writing of a particular function. It is not necessary to write the same logic in the whole program. Here only you need to write the function program to get the data from database tables.

23. What is a collation in SQL?

You can determine by the collation how character type data can be sorted and compared. Collation is defined as a set of rules.

24. Tell us about the advantages of a Stored Procedure?

Answer - In modular programming, you can use stored procedure it creates once but can use so many times whenever you require.  It is the stored procedure can support quicker execution instead of executing multiple queries; this reduces the transfer and manages the data.

25. Tell us about Union, minus and INTERSECT commands?

Answer – Here in order to combine two tables, the UNION operator is used. Its operator eliminates rows that are duplicated in the table. To return a row from the first query we use MINUS operator in SQL. To return rows returned by both the queries we use INTERSECT command.

conclusion

we hope this article will help you to get basic information about structured query language (SQL). If you are preparing an interview for a database then it would help you to understand SQL databases.