Lesson 16 · Turn the ERD into CREATE TABLE

Translate a requirement into a constraint

Task 1 of 2 · Disposable schema practice · 0 results checked · 0 explanations saved

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Read the idea

A table definition carries requirements: PRIMARY KEY identifies a record, NOT NULL requires a value, UNIQUE prevents repetition, CHECK constrains a value and DEFAULT supplies an omitted value.

Create parent tables before child tables. Enable PRAGMA foreign_keys = ON in a disposable SQLite database when testing FK rejection. A schema that loads still needs a data dictionary and tests.

Worked example

CREATE TABLE customers (id INTEGER PRIMARY KEY, email TEXT NOT NULL UNIQUE, name TEXT NOT NULL, phone TEXT);

Your task

Create customers with these columns in order: id INTEGER PRIMARY KEY; email TEXT NOT NULL UNIQUE; name TEXT NOT NULL; phone TEXT, which may be missing. Emails must be present and cannot be shared by two customers. Explain which requirement each constraint enforces.

Predict or plan before trying

Give me a hint

Use the question’s requirements as your checklist. State an assumption if the wording does not establish a rule.

Compare with a worked answer

CREATE TABLE customers (id INTEGER PRIMARY KEY, email TEXT NOT NULL UNIQUE, name TEXT NOT NULL, phone TEXT);

Using an answer is useful practice. Record what you learned; it does not demonstrate independent mastery.

Each run starts with a fresh disposable database. Include CREATE statements and test inserts together when experimenting. Check result expects your table definitions without added test rows.

Table & column names only · ↑ ↓ choose · Tab insert · Esc dismiss

Query results

Run your query to see the result here.

Explain your evidence

Why can phone be NULL while email cannot? What does UNIQUE add beyond NOT NULL?

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