SQL Databases: Extracting Data Like a Pro

By Prof. David Chen, CS Examiner·Updated April 18, 2026
A snippet of SQL code showing a SELECT and WHERE query executed on a relational database.

What is the exact structure of a 4-line CAIE SQL Query?

Every O-Level SQL query follows this exact pattern. 1) SELECT (the columns you want to output). 2) FROM (the exact name of the table). 3) WHERE (the conditions/filters using operators like >, <, AND, OR). 4) ORDER BY (the column to sort by, plus ASC or DESC). Memorize this 4-step sequence.

Table of Contents

SQL (Structured Query Language) is the industry standard for interacting with databases. In Paper 2, you must write completely accurate SQL scripts. If you miss a quotation mark around a string, you lose the mark. This guide from our Ultimate O-Level Computer Science Guide provides the exact syntax rules required by examiners.

1. The Database Vocabulary Trap

Before writing SQL, you must know what you are looking at. A relational database is a table of data, but CAIE uses very specific terminology.

  • Table / Relation: The entire grid of data.
  • Field / Column: A vertical column holding a specific TYPE of data (e.g., 'FirstName', 'Price').
  • Record / Row: A horizontal line holding all the data relating to ONE specific item or person (e.g., all data regarding Student ID 142).
  • Primary Key: A specific Field (column) where every entry is guaranteed to be 100% unique (e.g., a Passport Number or Barcode). It prevents duplicate data.

2. The 4-Step Query Builder

Assume we have a table called STUDENTS. It has fields: StudentID, Name, Age, and PassedExam.

The Question: "Write an SQL query to output the Names and Ages of all students who passed the exam, sorting the list from oldest to youngest."

SELECT Name, Age

-- We only ask for Name and Age. We do not ask for StudentID.

FROM STUDENTS

-- The exact name of the table.

WHERE PassedExam = TRUE

-- The filter condition.

ORDER BY Age DESC;

-- We want oldest first, so we sort the Age column by DESCending order.

💡 Tutor's Tip
Output All Fields: If the question asks to output "all details" or "all records", you do not need to type every column name. Just write SELECT *. The asterisk is the wildcard operator meaning 'everything'.

3. Mastering the WHERE Clause (Strings & Booleans)

The WHERE clause is where students lose the most marks. You must use the correct data types.

Rule 1: Text requires Quotes

If you are searching a string/text field, you MUST wrap the search term in single or double quotes. If you write WHERE City = London, it is a syntax error. It must be WHERE City = "London".

Rule 2: Numbers and Booleans do NOT

If you are filtering an Integer or Boolean, do not use quotes. E.g., WHERE Age > 18 or WHERE HasPaid = FALSE.

Rule 3: Using AND / OR

You can stack filters indefinitely. Be very careful with logic. To find expensive blue cars only, you write:
WHERE Color = "Blue" AND Price > 10000.

Prof. David Chen📋 From the Desk of Prof. David Chen
Never write the word "EQUALS" in your script. Use the actual = sign. The comparison operators allowed are: = (Equal), > (Greater than), < (Less than), >=, <=, and <> (Not Equal).

Frequently Asked Questions

What does the SELECT keyword do in SQL?▼
It defines which specific columns you want to extract and view in the final output.
How does the WHERE clause work?▼
It filters the table, only returning rows where a specific mathematical or logical condition is TRUE.
What is the difference between ASC and DESC in ORDER BY?▼
ASC sorts A-Z or smallest-to-largest. DESC sorts Z-A or largest-to-smallest.
What is a Primary Key?▼
A field holding unique, non-repeatable data (like an ID number) used to identify a specific row in the database.

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