SQL: WHERE & Logical Operators — AQA GCSE CS (8525)

Spec & Goals 3 min

AQA Spec 3.7.2 — Filtering records with WHERE; AND, OR and comparison operators

By the end of this lesson you can:

Use WHERE to return only records that meet a condition.
Use comparison operators (=, >, <, >=, <=, <>).
Combine conditions with AND and OR.

Warm-Up 5 min

SELECT chose the columns; now WHERE chooses the rows — returning only the records that match a condition.

Quick starter

To list only students in form 10A, what test must each row pass?

Reveal the idea

The Form field must equal '10A'. In SQL: WHERE Form = '10A'. Text values go in single quotes.

Key Concept — choosing rows 14 min

SELECT fields
FROM table
WHERE condition;

Only records where the condition is true are returned.

Comparison operators

Operator	Means	Example
`=`	equal to	`Form = '10A'`
`>` / `<`	greater / less than	`Mark > 80`
`>=` / `<=`	greater/less than or equal	`Mark >= 65`
`<>`	not equal to	`Town <> 'Ipoh'`

Key point: put text and dates in single quotes ('Penang'); numbers are written without quotes (80).

Combining conditions with AND / OR

AND — both conditions must be true.
OR — either condition may be true.

Reminder of the Student table:

StudentID	Name	Form	Town	Mark
101	Aisyah	10A	Ipoh	78
102	Wei Jie	10B	Penang	65
103	Priya	10A	Ipoh	91
104	Arjun	11C	Johor Bahru	54
105	Mei Ling	11C	Penang	88
106	Hafiz	10B	Kuala Lumpur	72

Exam tip: a common slip is forgetting the quotes around text, or using == (that's programming). SQL uses a single = for equality.

Worked Example — filter the students 12 min

Query 1: students who scored more than 80.

SELECT Name, Mark
FROM Student
WHERE Mark > 80;

Name	Mark
Priya	91
Mei Ling	88

Query 2: students in form 10A and from Ipoh.

SELECT Name
FROM Student
WHERE Form = '10A' AND Town = 'Ipoh';

Name
Aisyah
Priya

Query 3: students from Penang or Kuala Lumpur.

SELECT Name, Town
FROM Student
WHERE Town = 'Penang' OR Town = 'Kuala Lumpur';

Name	Town
Wei Jie	Penang
Mei Ling	Penang
Hafiz	Kuala Lumpur

How the marks are earned: correct WHERE field + operator + value (with quotes on text) earns the condition mark; the right AND/OR earns the combining mark.

Try It Yourself 12 min

🟢 Easy

Goal: Write a query for the names of all students in form 11C.

🟡 Medium

Goal: Write a query for students with a Mark of at least 70, showing Name and Mark.

🔴 Stretch

Goal: Write a query for students in form 10B who scored below 70. State the result rows.

📝 Exam Practice 10 min

Write a program[3 marks]

Write an SQL query to display the Name of every student whose Town is Penang.

Mark scheme

SELECT Name (1).
FROM Student (1).
WHERE Town = 'Penang'; — correct field, quotes and value (1).

Write a program[2 marks]

Write a query to list students in form 10A with a Mark over 75.

Mark scheme

SELECT ... FROM Student WHERE Form = '10A' (1).
AND Mark > 75; (1).

State[1 mark]

State the result of SELECT Name FROM Student WHERE Mark < 60;

Mark scheme

Arjun (only student with Mark below 60) (1).

Recap & Key Terms 3 min

WHERE filters rows by a condition. Use comparison operators (= > < >= <= <>), quoting text and dates but not numbers. Combine conditions with AND (both true) and OR (either true).

WHERE: The SQL clause that returns only records meeting a condition.
Comparison operators: =, >, <, >=, <=, <> — test a field against a value.
AND: Combines conditions so both must be true.
OR: Combines conditions so either may be true.

Homework 1 min

Task (≤ 15 min): Using the Student table, write queries for: (a) students not from Ipoh; (b) students in form 10A or 10B; (c) students with a mark between 70 and 90 (inclusive).

Model answer

-- (a)
SELECT Name FROM Student WHERE Town <> 'Ipoh';

-- (b)
SELECT Name FROM Student WHERE Form = '10A' OR Form = '10B';

-- (c)
SELECT Name, Mark FROM Student WHERE Mark >= 70 AND Mark <= 90;

Award marks for: correct use of <> (1); correct OR (1); correct AND range (1).