[9.4] SQL single-table queries

[9.4] SQL Single-Table Queries: SELECT, FROM, WHERE, ORDER BY, SUM, COUNT, AND, OR

Why learn SQL for a single table?

SQL (Structured Query Language) lets you ask questions about data stored in a database table and return exactly what you need. In the IGCSE you should be able to read, understand and complete short single-table SQL scripts that use the clauses and operators listed in this benchmark: SELECT, FROM, WHERE, ORDER BY with ASC/DESC, the aggregate functions SUM and COUNT, and the logical operators AND and OR.

Think of a database table as a spreadsheet with named columns. SQL is the precise way to filter rows, choose columns, sort results and calculate totals without changing the stored data. Small details matter: a missing condition, the wrong operator, or sorting in the wrong direction can change the answer. This page will show you the structure of each clause, common mistakes to avoid, and realistic patterns you will meet in questions.

A running example table

All examples refer to a single table called Orders with these fields:

Core SQL clause structure

Use this mental template for single-table queries:

• SELECT columns or expressions
• FROM TableName
• WHERE row condition optional
• ORDER BY column ASC/DESC optional

Add SUM or COUNT in the SELECT list when a total or number of rows is required. For this benchmark, totals are for the whole filtered set (no grouping across categories).

Reading, understanding, completing

Exam questions often show a partly written query with missing parts indicated by ???. Your job is to complete it correctly by using field names and the right operators. Always cross-check with the field list given in the question.

Tabs of targeted examples

• Filtering: Single condition in WHERE
• Combining conditions: AND vs OR
• Edge case: Operator precedence and brackets

SELECT OrderID, Customer, Qty
FROM Orders
WHERE City = 'Bristol';

SELECT OrderID, City
FROM Orders
WHERE City = 'Bristol' OR Qty > 5;

SELECT OrderID, Customer, City, Qty, OrderDate
FROM Orders
WHERE (City = 'Bristol' AND Qty > 5)
   OR OrderDate = '2026-03-14';

• ORDER BY ascending then descending
• Secondary sort key
• Edge case: Sorting numbers stored as text

SELECT Customer, Qty
FROM Orders
WHERE City = 'Bristol'
ORDER BY Qty DESC;

SELECT City, Customer
FROM Orders
ORDER BY City ASC, Customer ASC;

• SUM of a calculated expression
• COUNT rows that match a filter
• Edge case: COUNT(*) vs COUNT(column)

SELECT SUM(Qty * PriceEach) AS TotalRevenue
FROM Orders
WHERE City = 'Bristol';

SELECT COUNT(*) AS NumOrders
FROM Orders
WHERE OrderDate = '2026-03-14';

Checklist for completing SQL in the exam

1. Identify fields exactly as given. SQL is sensitive to spelling of field names.
2. Choose operators carefully: =, >, <, and use AND/OR to match the English meaning.
3. Quote text values with single quotes. Do not quote numbers or dates if the exam board shows date as text, follow their format exactly.
4. Calculate inside SELECT using expressions such as Qty * PriceEach when totals are needed.
5. Sort only if the question asks for a specific order. State ASC or DESC if not obvious.
6. Test logic by paraphrasing: “I am selecting these columns from this table where this condition is true, then ordering by this column.”

Deep Dive: Translating English questions into SQL

Underline the output columns, circle the filter words, and box any sorting phrases. For totals, look for verbs like “total”, “sum”, or “how many”. Then map them to clauses: outputs to SELECT, table name to FROM, filters to WHERE (with AND/OR), sorting to ORDER BY, and totals to SUM/COUNT. Finally, check the units and directions, e.g. “highest first” means DESC.