Excellent Consultancy Pvt. Ltd. maintains two tables fo — CBSE Class 12 Informatics Practices 2024 PYQ

Question

Excellent Consultancy Pvt. Ltd. maintains two tables for all its employees.

Table : Employee

Employee_id	First_name	Last_name	Salary	Joining_date	Department
E101	Monika	Das	100000	2019-01-20	Finance
E102	Mehek	Verma	600000	2019-01-15	IT
E103	Manan	Pant	890000	2019-02-05	Banking
E104	Shivam	Agarwal	200000	2019-02-25	Insurance
E105	Alisha	Singh	220000	2019-02-28	Finance
E106	Poonam	Sharma	400000	2019-05-10	IT
E107	Anshuman	Mishra	123000	2019-06-20	Banking

Table : Reward

Employee_id	Date_reward	Amount
E101	2019-05-11	1000
E102	2019-02-15	5000
E103	2019-04-22	2000
E106	2019-06-20	8000

Write suitable SQL queries to perform the following task : (i) Change the Department of Shivam to IT in the table Employee. (ii) Remove the record of Alisha from the table Employee. (iii) Add a new column Experience of integer type in the table Employee. (iv) Display the first name, last name and amount of reward for all employees from the tables Employee and Reward. (v) Display first name and salary of all the employees whose amount is less than 2000 from the tables Employee and Reward. OR Write suitable SQL queries for the following task : (i) Display the year of joining of all the employees from the table Employee. (ii) Display each department name and its corresponding average salary. (iii) Display the first name and date of reward of those employees who joined on Monday from the tables Employee and Reward. (iv) Display sum of salary of those employees whose reward amount is greater than 3000 from the tables Employee and Reward. (v) Remove the table Reward.

CBSECBSE Class XII Board 2024Subjective· 5mImportance★★★★★

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Part (a)Concept understanding — Database Querying

Database Querying: Asking Questions of a Data Collection

Think of a library. You walk in, and instead of wandering through endless shelves, you go to the librarian and say: "I need all books by R. K. Narayan published after 1980." The librarian knows exactly where to look, finds the relevant books, and hands you a short list. That act of asking — of specifying exactly what you want from a large, organised collection — is the essence of querying.

A database is like that library, but for digital information. It stores data in a structured way, typically in tables with rows and columns. A query is simply a question you ask of that database. You don't need to know where the data lives or how it's stored internally. You just need to state what you want.

The Precise Meaning

In formal terms, a database query is a request for data or information from a database. The request is written in a special language that the database understands. The most common such language is SQL (Structured Query Language), but the concept of querying exists in every database system.

When you query a database, you are doing one of four things:

Retrieving data (the most common — "show me the customers who live in Delhi")
Inserting new data ("add this new student record")
Updating existing data ("change this address")
Deleting data ("remove this old order")

For a commerce or humanities student, the retrieval part is where the real power lies. You are not just pulling out raw data — you are filtering, sorting, and combining it to get answers.

Why It Matters

A database without querying is like a library with the lights off. The data exists, but you cannot use it. Querying turns stored facts into actionable information.

Consider a small business owner who keeps customer records in a spreadsheet. Without querying, they might scroll through hundreds of rows to find customers who haven't purchased in six months. With a query, they type one request and get the answer instantly. That answer might lead to a targeted marketing campaign, which brings in revenue.

Note

Querying is not about memorising commands. It is about thinking in terms of conditions and relationships. The skill is learning to translate a real-world question — "Which products are out of stock?" — into a precise, unambiguous request the database can process.

The Intuition Behind It

Every query has a simple structure at its core:

What data do you want? (Which columns or fields?)
Where is it? (Which table or collection?)
Under what conditions? (Which rows match your criteria?)

If you can answer those three questions in plain English, you are already thinking like someone who queries databases. The technical language (SQL) is just a way to write those answers down so the computer understands.

A Real-World Example …

Part (b)Concept understanding — Database Querying

Database Querying: Asking Questions of a Data Collection

The Precise Meaning

When you query a database, you are doing one of four things:

Retrieving data (the most common — "show me the customers who live in Delhi")
Inserting new data ("add this new student record")
Updating existing data ("change this address")
Deleting data ("remove this old order")

For a commerce or humanities student, the retrieval part is where the real power lies. You are not just pulling out raw data — you are filtering, sorting, and combining it to get answers.

Why It Matters

A database without querying is like a library with the lights off. The data exists, but you cannot use it. Querying turns stored facts into actionable information.

Note

The Intuition Behind It

Every query has a simple structure at its core:

What data do you want? (Which columns or fields?)
Where is it? (Which table or collection?)
Under what conditions? (Which rows match your criteria?)

A Real-World Example …

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Part (a)

-- (i) change Shivam's department to IT
UPDATE Employee SET Department='IT' WHERE First_name='Shivam';

-- (ii) remove Alisha's record
DELETE FROM Employee WHERE First_name='Alisha';

-- (iii) add integer column Experience
ALTER TABLE Employee ADD Experience INT;

-- (iv) first name, last name and reward amount for all employees
SELECT E.First_name, E.Last_name, R.Amount
FROM Employee E LEFT JOIN Reward R ON E.Employee_id=R.Employee_id;

-- (v) first name and salary where reward amount < 2000
SELECT E.First_name, E.Salary
FROM Employee E INNER JOIN Reward R ON E.Employee_id=R.Employee_id
WHERE R.Amount < 2000;
``` …

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Part (a): UPDATE, DELETE, ALTER ADD, LEFT JOIN, and filtered INNER JOIN. Part (b): YEAR(), GROUP BY AVG, Monday-join (0 rows), SUM(Salary) where Amount>3000 = 1000000, DROP TABLE.

Part (a)

(i) Modify one row with UPDATE, identifying Shivam:

UPDATE Employee SET Department='IT' WHERE First_name='Shivam';

(ii) Remove a row with DELETE:

DELETE FROM Employee WHERE First_name='Alisha';

(iii) Add a new integer column with ALTER TABLE:

ALTER TABLE Employee ADD Experience INT;

(iv) "For all employees" means every employee must appear even without a reward, so use a LEFT JOIN on Employee_id; missing rewards show NULL.

(v) "Whose amount is less than 2000" needs a reward, so an INNER JOIN with WHERE Amount<2000. From the data only E101 (Monika, reward 1000) qualifies; E103's reward is exactly 2000, which is not less than 2000.

UPDATE Employee SET Department='IT' WHERE First_name='Shivam';
DELETE FROM Employee WHERE First_name='Alisha';
ALTER TABLE Employee ADD Experience INT;
SELECT E.First_name, E.Last_name, R.Amount
FROM Employee E LEFT JOIN Reward R ON E.Employee_id=R.Employee_id;
SELECT E.First_name, E.Salary
FROM Employee E INNER JOIN Reward R ON E.Employee_id=R.Employee_id
WHERE R.Amount < 2000; …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2024Set 91/41 markMCQ
$Q. The SELECT statement when combined with ____ clause, returns records without repetition. (A) DISTINCT (B) DESCRIBE (C) UNIQUE (D) NULL$
›Reveal solutionSolution
SQL's DISTINCT keyword filters out duplicate rows from query results, ensuring each record appears only once. The answer is (A).

When you query a database table, you often retrieve multiple rows that may contain identical values across all selected columns. Think of a customer orders table where the same customer ID appears dozens of times—one for each order. If you only want to see which customers have placed orders (not how many times), you need a mechanism to collapse duplicates into a single representative row.

The SELECT statement by itself returns every row that matches your conditions, duplicates and all. SQL provides the DISTINCT keyword specifically to eliminate repetition: it compares the entire result set row-by-row and keeps only unique combinations.

How each option relates to SQL

DISTINCT – This is the standard SQL keyword placed immediately after SELECT to remove duplicate rows. For example:

SELECT DISTINCT customer_id FROM orders;

returns each customer ID exactly once, no matter how many orders they placed.

DESCRIBE – A command (or keyword in some databases) used to show the structure of a table—its column names, data types, constraints—not to filter query results. It's a metadata inspection tool, not a result-set modifier.

UNIQUE – In SQL, UNIQUE is a constraint applied to columns during table creation to enforce that no two rows have the same value in that column. It's not a clause you combine with SELECT to filter results. You might see it in:

CREATE TABLE users (email VARCHAR(100) UNIQUE); …
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CBSE 2020Set 91/D1 mark
$Q. Which clause is used with a SELECT command in SQL to display the records in ascending order of an attribute?$
›Reveal solutionSolution
The ORDER BY clause is used with the SELECT command in SQL to display records in ascending order of an attribute.

When we work with databases using SQL (Structured Query Language), the SELECT command is our primary tool for retrieving information. Imagine a vast library of books; SELECT is like asking the librarian to fetch specific books or details about them. However, when the librarian hands you the books, they might not be in any particular order – perhaps by the order they were found, or by some internal system. For us to make sense of the data, especially when dealing with many records, we often need them arranged in a logical sequence.

This need for structured presentation is where ordering comes in. Displaying records in ascending order of an attribute means arranging them from the smallest value to the largest, or alphabetically from A to Z for text. For instance, if you're looking at a list of students, you might want them sorted by their roll numbers from lowest to highest, or by their names alphabetically. This makes the data much easier to read, analyze, and understand.

To achieve this specific ordering in SQL, we use a special clause called ORDER BY. This clause is appended to the SELECT statement and tells the database system exactly how we want the retrieved records to be sorted.

Important

The ORDER BY clause is crucial for presenting query results in a meaningful and organized manner, making data analysis and reporting much more efficient.

Here's how the ORDER BY clause works:

Specifying the Attribute: You must specify one or more attributes (columns) by which you want to sort the data. For example, if you have a table of Students with columns like RollNo, Name, and Marks, you could choose to sort by RollNo or Name.

Ascending Order (ASC): By default, if you just specify an attribute with ORDER BY, the records will be sorted in ascending order. However, it's good practice to explicitly use the ASC keyword to make your intention clear. ASC stands for Ascending. This means numbers will go from smallest to largest, and text will go from A to Z. …
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Part (a)

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