LEFT JOIN keeps everyone

Read first Task 22

LEFT JOIN keeps every left-table row, even when there is no match.

What you are building

The task in front of you: What does LEFT JOIN keep?.

The editor already holds a working starting point. Do not delete it and start again — read it, change one thing, run it, and watch which check moves. That loop is the whole method.

Why this matters

You are inside the section “Section 3 · Joins and subqueries” of the SQL & Databases track. Everything in this section builds towards the section project, and this task is one of the pieces that project leans on.

In real work nobody marks your code — it either runs or it does not, and someone is waiting for the result. The checks here are deliberately strict about output, because a program that prints the right thing in the wrong shape fails in the real world too.

The key idea

SQL describes the result you want, not the steps to get it. SELECT picks columns, FROM picks the table, and WHERE filters rows before they are returned.

Quotes matter: text needs single quotes, numbers do not. A column name in the wrong place is the most common reason a correct-looking query returns nothing.

Two mistakes to avoid

Filtering with WHERE after a JOIN when you meant to filter before it — the rows you excluded still influenced the join.
Writing SELECT * and then comparing text output. Ask for exactly the columns the task names, in the order it names them.

What the automatic checks look for

The right-hand column runs 1 check every time you press Run code. Nothing is hidden:

The output has to contain “rows:[["Sara",11667],["S…”.

Task

What does LEFT JOIN keep?

The editor already contains a starting point. Change it until every check passes — the Next task button unlocks when it does.

What you start with

SELECT students.name, fees.amount FROM students LEFT JOIN fees ON fees.student_id = students.id;

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 3 · Joins and subqueries

Code editor Ctrl + Enter runs

SELECT students.name, fees.amount FROM students LEFT JOIN fees ON fees.student_id = students.id;

Run your code to see the output and the checks.

Your result

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Checks on this task:

Check 1

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LEFT JOIN keeps everyone