Database Management · Intermediate level

Intermediate level · Module 1: Database Design and Normalisation · Lesson 2 of 3

Normalisation to Third Normal Form

Remove repetition and anomalies by normalising tables step by step.

In this lesson you will

  • Identify update, insert and delete anomalies
  • Normalise a table to 1NF, 2NF and 3NF

Key concepts

anomalyfirst normal formsecond normal formthird normal form

The lesson

A flat table that repeats data causes anomalies: change a village name in one row but not another (update anomaly), cannot record a village until it has a household (insert anomaly), lose a village when its last household is deleted (delete anomaly).

First normal form: each cell holds one value and there are no repeating groups such as member1, member2. Second: every non-key column depends on the whole key. Third: non-key columns depend only on the key, not on other non-key columns — a village's county belongs in a villages table, not in households.

Normalised designs store each fact once. For reporting you may later create views or summary tables, but the core data should be normalised.

Step by step

  1. Find anomalies in the provided flat spreadsheet.
  2. Bring it to 1NF by splitting repeating groups.
  3. Move partial dependencies out for 2NF.
  4. Move transitive dependencies out for 3NF.

Practice activity

Normalise the NGO's flat registration spreadsheet into third normal form tables.

Expected result: A set of tables where each fact is stored once and the anomalies are gone.

Check your understanding

  1. What is an update anomaly?

    Show answer

    Changing a repeated fact in one place but not others, leaving inconsistent data.

  2. What does third normal form remove?

    Show answer

    Columns that depend on other non-key columns rather than on the key.

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