Databases and SQL I · Lesson 02 / 12

Model with rules

Read a schema and distinguish identity, required values, uniqueness and limits.

Let's discover together

1
Read schema.sql. kits describes materials; loans records events. Separating them avoids repeating all material attributes for each loan. Start with the questions and rules your model must support.
2
PRIMARY KEY identifies a row. code is UNIQUE and NOT NULL: it cannot repeat or be missing. label may repeat. stock uses CHECK to require a nonnegative integer after SQLite affinity conversion; INTEGER alone is insufficient in an ordinary table.
3
NULL means missing or unknown, not zero or empty text. CHECK can accept NULL when its expression is not false; add NOT NULL for required data. Database rules complement application validation.
4
The example creates a practice table in memory. On separate runs, repeat an id and try negative stock. Read the violated constraint; do not remove it just to make the command pass.

Your data workbench

Our model: kits.id ← loans.kit_id. One material can have many loans; names may repeat. We use fictional data only.

Predict before opening the reference. It shows verified output from the original example, not execution of your text. Run your changes with the kit on your computer.

-- Model with rules
CREATE TABLE practice (id INTEGER PRIMARY KEY, code TEXT NOT NULL UNIQUE, stock INTEGER NOT NULL CHECK(typeof(stock)='integer' AND stock>=0));
INSERT INTO practice VALUES(1,'T-01',0);
SELECT id, code, stock FROM practice ORDER BY id;

Compare with reference output

[
  {
    "columns": [
      "id",
      "code",
      "stock"
    ],
    "rows": [
      [
        1,
        "T-01",
        0
      ]
    ]
  }
]

Run the command in the extracted folder’s terminal. Use python3 on macOS/Ubuntu or py if that is your Windows launcher. Every run starts in memory; read README.md for saving files and recovery practice.

python lab.py run lesson.sql

My files and GitHub

The editor saves your .sql draft in this browser. Download it and replace lesson.sql in the kit; for the final project, availability.sql. The ZIP remains the original template. GitHub publishing sends only the confirmed file, without executing SQL or sending a database.

Official links and next step

Official documentation

✦

YOUR MISSION

Read a schema and distinguish identity, required values, uniqueness and limits.

Take it with you

Design a fictional hobby-object table. Explain its key, an optional value and two rejected values.

At your own pace

My files and GitHub

Every lesson can become your own record: code, notes or a practice plan. Saving a file to GitHub is optional and does not change your XP.

Student guide

The editor and downloads open when this lesson is available to your account. Check access below or return to the track map.

Checking your access to this lesson…

Your path, step by step

Download activity materials

Download the lesson example and a workbook for your notes. The ZIP includes a guide to organizing activities in one or more repositories. Publishing is optional; eligible accounts can also use the GitHub upload button.

Your file for this lesson

Edit the example or record what you learned. This space does not run code or grade answers. The draft is saved only in this browser, separately per account; you choose when to download or upload to GitHub.

The example may be only a snippet or outline. Changing the extension does not make it a complete program. The activity ZIP contains starting material; the edited-file button downloads your text.

My code or notesFile format

Your text will be saved in this browser when you edit it. On a shared computer, clear your drafts when finished.

Direct upload accepts up to 8 KiB of text in one file. Use downloads and the manual guide for projects with multiple files.

Model with rules

Let's discover together

Your data workbench

Official links and next step

Now it's your turn

Read, predict and check

Take it with you

My files and GitHub

Your file for this lesson

Save to my GitHub

Rullstpetbot