AI Computer Science Academy · Faisalabad

SQL & Databases

Indexes

Task 42 of 56 SQL Section 5 · Real academy queries
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Indexes

An index speeds up lookups on a column.

Definition and example

Indexes is the focus of this lesson. An index speeds up lookups on a column. The task asks you to apply that idea in a small example: Why create an index. Before you run the code, predict what should happen. Then Inspect the returned columns and rows and compare it with your prediction. If the result differs, change one relevant line and run it again. Testing one change at a time makes the cause of a result easier to understand.

The sample database 
CREATE TABLE courses (id INTEGER PRIMARY KEY, title TEXT, monthly_fee INTEGER);
CREATE TABLE students (id INTEGER PRIMARY KEY, name TEXT, city TEXT, course_id INTEGER, joined TEXT);
CREATE TABLE fees (id INTEGER PRIMARY KEY, student_id INTEGER, month TEXT, amount INTEGER, paid INTEGER);

INSERT INTO courses VALUES (1,'Web Design',9000),(2,'Python',11667),(3,'JavaScript',11667),(4,'AI & Prompt Engineering',15000);
INSERT INTO students VALUES
 (1,'Sara','Faisalabad',2,'2026-01-12'),
 (2,'Ali','Faisalabad',1,'2026-01-20'),
 (3,'Hina','Jhumra',2,'2026-02-02'),
 (4,'Bilal','Faisalabad',4,'2026-02-15'),
 (5,'Ayesha','Sargodha',3,'2026-03-01'),
 (6,'Usman','Jhumra',1,'2026-03-11'),
 (7,'Zainab','Faisalabad',4,'2026-04-05'),
 (8,'Hamza','Faisalabad',3,'2026-04-19');
INSERT INTO fees VALUES
 (1,1,'2026-01',11667,1),(2,1,'2026-02',11667,1),
 (3,2,'2026-01',9000,1),(4,2,'2026-02',9000,0),
 (5,3,'2026-02',11667,1),(6,3,'2026-03',11667,0),
 (7,4,'2026-02',15000,1),(8,4,'2026-03',15000,1),
 (9,5,'2026-03',11667,0),
 (10,6,'2026-03',9000,1),(11,6,'2026-04',9000,0),
 (12,7,'2026-04',15000,0),
 (13,8,'2026-04',11667,1);
SQL 1 automatic check Section 5 · Real academy queries
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