Primary key and foreign key

Code pattern

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Definition

A primary key uniquely identifies each record in a table; a foreign key is a field that holds another table's primary key to link the tables.

Example: ClassID is the primary key of Class and a foreign key in Student.

Found in: course specifications, school notes.

Where you'll use it in the test

Syllabus area: Y12 Programming for the Web.

Question types it can appear in

Multiple choice: Pick the option that matches the definition or example.
Fill in the blanks: Choose this term to complete a statement or table.
Drawing: ERD
SQL: Write or read it in the SQL query tool.

Where it has appeared in the paper

Programming for the Web (Part C); The Software Engineering Project (Part A). Part letters follow each paper’s own layout.

How to use it

A model sentence

General advice, built from the definition and example above

Code pattern: “A primary key uniquely identifies each record in a table; a foreign key is a field that holds another table's primary key to link the tables.” Then apply it: ClassID is the primary key of Class and a foreign key in Student.

In a short answer, give the definition in your own words first, then tie it to the situation in the question. Do not copy the example above unless it fits the scenario.

Official worked answer

Familiarisation Q12b (3 marks): SQL (joins, AS) (3 marks): official criteria and sample answer

Criteria

3: Correct SQL query. 2: Substantially correct query with at least TWO of: renaming the columns; selecting the three tables; joining the tables. 1: Some understanding of renaming the columns or joining the tables.

Sample answer

SELECT Customers.CustName as 'Customer', Products.ProductName as 'Product', Orders.OrderQuantity as 'Quantity' FROM Products, Customers, Orders WHERE Orders.ProductID = Products.ProductID AND Orders.CustID = Customers.CustID ORDER BY Orders.OrderID ASC

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Go deeper

Flashcard: Primary key and foreign key in Programming for the Web (Year 12) · study that set
Memorise: SQL vs ORM
Full term page: every question, note and marking comment for Primary key and foreign key

Check yourself

Write or say the “Primary key and foreign key” pattern from memory: the syntax and what it does.

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