Consider a database name "db_name" whose attributes are intern_id (primary key), subject.
Intern_id = {1, 2, 3, 4, 5, 6}
Subject = {sql, oop, sql, oop, c, c++}
If these are one to one relation then what will be the output of the following MySQL statement?

SELECT intern_id
FROM db_name
WHERE subject IN (c, c++, oop);

Solution (By Examveda Team)

This question asks you to understand how MySQL selects data from a database table based on specific conditions. Let's break it down step by step:
1. The Database Table:
We have a table named "db_name" with two columns:
* intern_id: This column holds unique identification numbers for interns (e.g., 1, 2, 3, ...). It's the primary key, meaning each intern_id is unique and identifies a single row in the table.
* subject: This column represents the subject an intern is learning (e.g., 'sql', 'oop', 'c', 'c++').
2. The Relationship:
The question states that the relationship between intern_id and subject is one-to-one. This means that each intern can only be associated with a single subject, and each subject can only be associated with one intern.
3. The MySQL Statement:
The given SQL statement is:
```sql SELECT intern_id FROM db_name WHERE subject IN (c, c++, oop); ```
Let's explain what each part does:
* SELECT intern_id: This part tells MySQL to retrieve the values from the 'intern_id' column.
* FROM db_name: This indicates that the data should be retrieved from the table named "db_name".
* WHERE subject IN (c, c++, oop): This is the crucial part that filters the data. It says, "Only retrieve rows where the 'subject' column has a value of 'c', 'c++', or 'oop'."
4. Finding the Output:
Now, let's look at the data and apply the filter:
* Intern_id: {1, 2, 3, 4, 5, 6}
* Subject: {sql, oop, sql, oop, c, c++}
Based on the filter, we need to find the 'intern_id' values that have subjects 'c', 'c++', or 'oop'. Looking at the data, we find the following:
* Intern_id 5 has the subject 'c'.
* Intern_id 6 has the subject 'c++'.
* Intern_id 2 has the subject 'oop'.
* Intern_id 4 has the subject 'oop'.
Therefore, the output of the SQL statement will be: {2, 4, 5, 6}.
Correct Answer: Option D: {2, 4, 5, 6}