Chapter 12: Structured Query Language (SQL) Class 12 Computer Science NCERT Solutions

Structured Query Language (SQL) is the standard language for managing and manipulating relational databases. In Chapter 12 – SQL, students dive into practical database interaction, writing queries to create tables, insert data, update records, and retrieve meaningful information using various SQL commands.

What You Will Learn in Chapter 12

This chapter focuses on hands-on SQL usage, teaching students how to use SQL statements to manage databases. It includes data definition, manipulation, and query operations along with filtering, sorting, pattern matching, and aggregate functions.

Key Topics Covered

SQL Categories

• DDL (Data Definition Language): CREATE, ALTER, DROP
• DML (Data Manipulation Language): INSERT, UPDATE, DELETE
• DQL (Data Query Language): SELECT

Creating Tables Using SQL

CREATE TABLE Employee (
  EmpID INT PRIMARY KEY,
  Name VARCHAR(50),
  Salary INT,
  Department VARCHAR(30)
);

Inserting Records

INSERT INTO Employee VALUES (101, \'Anjali\', 50000, \'HR\');
INSERT INTO Employee VALUES (102, \'Ravi\', 60000, \'IT\');

Selecting Data

SELECT * FROM Employee;
SELECT Name, Salary FROM Employee WHERE Department = \'IT\';

Updating and Deleting Records

UPDATE Employee SET Salary = 70000 WHERE EmpID = 102;
DELETE FROM Employee WHERE EmpID = 101;

Filtering Data Using WHERE Clause

• SELECT * FROM Employee WHERE Salary > 50000;
• SELECT * FROM Employee WHERE Department = \'IT\' AND Salary >= 60000;

Pattern Matching with LIKE

• SELECT * FROM Employee WHERE Name LIKE \'A%\'; – Names starting with A
• SELECT * FROM Employee WHERE Name LIKE \'_a__\'; – Names with \’a\’ as second letter

Using IN, BETWEEN, IS NULL

• SELECT * FROM Employee WHERE Department IN (\'HR\', \'IT\');
• SELECT * FROM Employee WHERE Salary BETWEEN 40000 AND 70000;
• SELECT * FROM Employee WHERE Department IS NULL;

Sorting Records

SELECT * FROM Employee ORDER BY Salary DESC;
SELECT * FROM Employee ORDER BY Department ASC, Salary DESC;

Aggregate Functions

SQL supports built-in aggregate functions to perform calculations on data.

• SELECT COUNT(*) FROM Employee; – Total number of records
• SELECT AVG(Salary) FROM Employee; – Average salary
• SELECT MAX(Salary), MIN(Salary) FROM Employee; – Max and Min salary
• SELECT SUM(Salary) FROM Employee; – Total salary payout

Grouping Data Using GROUP BY

SELECT Department, COUNT(*) FROM Employee GROUP BY Department;
SELECT Department, AVG(Salary) FROM Employee GROUP BY Department;

Using HAVING Clause

SELECT Department, AVG(Salary)
FROM Employee
GROUP BY Department
HAVING AVG(Salary) > 55000;

Practice Table – Sample Data

Important SQL Output Questions

• Write SQL queries to display records based on conditions
• Predict the output of SELECT queries with WHERE, ORDER BY, LIKE
• Output-based MCQs with GROUP BY and HAVING

Common Errors in SQL Queries

• Missing commas in column list
• Incorrect string comparison syntax
• Wrong use of WHERE vs HAVING
• Using aggregate functions without GROUP BY

Download PDF – Chapter 12 SQL Solutions

Includes:

• Textbook-based SQL queries with answers
• Sample tables and query-based outputs
• MCQs and assertion-reason questions on SQL
• Error identification and correction practice

Preparation Tips for SQL

• Memorize syntax of SELECT, WHERE, ORDER BY, GROUP BY
• Practice on paper and database apps like MySQL or SQLite
• Understand logical flow of filters and aggregations
• Solve output-based and query writing questions daily

Additional Resources

• SQL Practice Sheets: Query writing exercises
• Online SQL Editors: Try code live on platforms like db-fiddle
• Flashcards: SQL functions and syntax reminders
• Sample Practical Exams: Realistic school-level SQL tasks

Conclusion

SQL is a vital skill for anyone interested in data, development, or IT. Chapter 12 equips students with powerful tools to manipulate and query data using SQL. With strong command over SQL queries, pattern matching, and grouping logic, students will be ready for board exams and real-world database work.