CHAPTER 17: VISUAL LABS 17a AND 17b

These original exercises use the same synthetic Harbour dataset as the book.
The display/check runner opens companion/sql/harbour.db read-only.
If that file is missing, first follow Chapter17 and run sql/setup_database.py.

RUN
1. Open walkthrough.py in IDLE and choose Run > Run Module (F5).
2. Alternatively, open a terminal in this ch17 folder.
   Windows: py walkthrough.py
   macOS/Linux: python3 walkthrough.py
Use the Python command that already worked in your setup.
No network access or third-party package is required.

The .sql files hold inspectable questions. The supplied Python wrapper prints
results and checks the original expected values. Before editing, predict the
new result. After editing, compare it manually; an old assertion may now fail
because your intentional change needs a different expected answer. Do not
remove a failed check until you can explain the changed result.

EXPECTED RESULTS AND PRACTICE
17a returns four campaign rows with two columns. 17b deliberately reports no such column: campaigns_name, then its corrected file returns the same four rows. Change/predict/check: change only SELECT to channel, campaign_name. The row count stays four and the first row becomes Paid search | Spring search. change_check.sql checks that exact result. If a correction seems ignored, save the SQL and check which file copy the runner reads.
