Top 6 SQL Interview Questions for Developers

 SQL or Structured Query Language is an extensively used database management system. Analysing and accessing data is the need of the hour, and SQL allows you to do just that. Attending an interview, more often than not, seems like an intimidating situation to be in. But, if you prepare well and are aware of the questions that may be asked during the interview process, it becomes easier for you to do well. There is a high demand for individuals who possess SQL skills. Thus, it becomes essential that you prepare well. Here are some of the top sql interview questions that are asked to a developer with SQL skills. 




 

Top SQL Interview Questions for Developers:

 

1. How do you find duplicate records in SQL?

 

There are several ways to find duplicate records in SQL. One method is to use the groupby function, and another way is to use the rank function. Let us understand this with the help of an example. 

 

While using Groupby:

SELECT 

    a, 

    b, 

    COUNT(*) occurrences

FROM w1

GROUP BY

    a, 

    b

HAVING 

    COUNT(*) > 1;

 

While using rank:

SELECT * FROM ( SELECTstudentid, name, age, Row_Number() OVER(PARTITION BY name, age ORDER By name) AS Rank FROM students ) AS X WHERE Rank>1

2. What do you mean by case WHEN in SQL?


Have you learnt any other programming languages? If yes, you will be aware of if-else statements. The WHEN case in SQL can be considered analogous to the if-else statement. In this case, multiple conditions are available to us, and we need to choose a particular thing based on these conditions. The syntax used for the case WHEN is:
CASE

    WHEN condition3 THEN result3

    WHEN condition4 THEN result4

    WHEN conditionA THEN resultA

    ELSE result

END;

You must first start by entering the CASE keyword that is followed by multiple WHEN, THEN statements. 

3. How do you create an index in SQL? 

To create an index in SQL, you must use the following command.

CREATE INDEX index_name

ON table_name (column3, column4, column5 ...);

You will start by using the keyword CREATE INDEX, followed by the name of the index, and then, use the ON Keyword. After the ON Keyword, we will mention the name of the table where we want to create this index. Finally, we must list the columns that will be present in the index. Let us understand this with the help of an example:

CREATE INDEX marks

ON Students (marks);

In this example, we created an index known as marks on top of the ‘marks’ column of the table ‘students’. Let us now understand how we can create a unique index. This is the syntax to be followed:

CREATE UNIQUE INDEX index_name

ON table_name (column4, column5,column6 ...);

 

You will start by using the keywords CREATE UNIQUE INDEX. Followed by the name of the index. After that, we will write the ON keyword followed by the name of the table. Lastly, in parenthesis, we will write the list of the columns on which we would want this unique index.

4. What is the main difference between SQL and NoSQL? 

SQL deals with relational databases. It stands for structured query language. SQL is mainly used for querying data from relational databases. Whereas, NoSQL works with non-relational databases. 

5. How would you find the second highest marks in a table in SQL? 

The syntax followed to find the second highest marks in an SQL table, is as follows.

SELECT name, MAX(marks)

  FROM students

 WHERE marks < (SELECT MAX(marks)

                 FROM students);

6. What do you mean by cursor in SQL? 

A cursor in SQL is used to store the database tables. The two main types of cursors available in SQL are: Implicit Cursor and Explicit Cursor. Let us understand these in detail. 

Implicit Cursor- It is the type of cursos that is default by nature. It is automatically created, and the user has no way to create this cursor. 

Explicit Cursor- These are user-defined. An explicit cursor can be created with the help of the following syntax:

DECLARE cursor_name CURSOR FOR SELECT * FROM table_name

First, we must use the keyword DECLARE. After this, we can write the name of the cursor, followed by the keyword CURSOR FOR SELECT*FROM, followed by the table name. 

Conclusion 

This brings us to the end of the blog on Top SQL Interview Questions for Developers. We hope that you found this helpful and are now better-equipped to ace your upcoming interviews. Happy Learning, and good luck!

 

Post a Comment

0 Comments