Suman has created a table named WORKER with a set of records to maintain the data of the construction sites, w

Question 62 of 95

Q. Suman has created a table named WORKER with a set of records to maintain the data of the construction sites, which consists of WID, WNAME, WAGE, HOURS, TYPE, and SITEID. After creating the table, she entered data in it, which is as follows : WID WNAME WAGE HOURS TYPE SITEID W01 Ahmed J 1500 200 Unskilled 103 W11 Naveen S 520 100 Skilled 101 W02 Jacob B 780 95 Unskilled 101 W15 Nihal K 560 110 Semiskilled NULL W10 Anju S 1200 130 Skilled 103

(a) Based on the data given above, answer the following questions :

(i) Write the SQL statement to display the names and wages of those workers whose wages are between 800 and 1500.

(ii) Write the SQL statement to display the record of workers whose SITEID is not known.

(iii) Write the SQL statement to display WNAME, WAGE and HOURS of all those workers whose TYPE is 'Skilled'.

(iv) Write the SQL statement to change the WAGE to 1200 of the workers where the TYPE is "Semiskilled"

(OR)

(b) Considering the above given table WORKER, write the output on execution of the following SQL commands:

(i) SELECT WNAME, WAGE*HOURS FROM WORKER WHERE SITEID = 103;

(ii) SELECT COUNT(DISTINCT TYPE) FROM WORKER ;

(iii) SELECT MAX(WAGE), MIN(WAGE), TYPE FROM WORKER GROUP BY TYPE;

(iv) SELECT WNAME, SITEID FROM WORKER WHERE TYPE="Unskilled" ORDER BY HOURS;

Uttarakhand UbseCBSE Class XII Board 2025Subjective· 4mImportance★★★★★

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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) names and wages where wage is between 800 and 1500
SELECT WNAME, WAGE FROM WORKER WHERE WAGE BETWEEN 800 AND 1500;

-- (ii) records where SITEID is unknown (NULL)
SELECT * FROM WORKER WHERE SITEID IS NULL;

-- (iii) WNAME, WAGE, HOURS of Skilled workers
SELECT WNAME, WAGE, HOURS FROM WORKER WHERE TYPE = 'Skilled';

-- (iv) change WAGE to 1200 for Semiskilled workers
UPDATE WORKER SET WAGE = 1200 WHERE TYPE = 'Semiskilled'; …

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Part (a): four SQL statements — BETWEEN range, IS NULL, TYPE filter, and an UPDATE.

Part (b): outputs — (i) 300000 & 156000; (ii) 3; (iii) per-type max/min wages; (iv) Jacob B/101 then Ahmed J/103.

Part (a)

(i) Wages between 800 and 1500 (inclusive) — BETWEEN is inclusive of both bounds:

SELECT WNAME, WAGE FROM WORKER WHERE WAGE BETWEEN 800 AND 1500;

(ii) "Not known" means the value is NULL; NULL is tested with IS NULL, never =:

SELECT * FROM WORKER WHERE SITEID IS NULL;

(iii) Skilled workers only:

SELECT WNAME, WAGE, HOURS FROM WORKER WHERE TYPE = 'Skilled';

(iv) Modify existing rows with UPDATE ... SET ... WHERE:

UPDATE WORKER SET WAGE = 1200 WHERE TYPE = 'Semiskilled'; …

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Part (a)

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