UofT-DSI | SQL - Assignment 2

[ruokun-ai]

What changes are you trying to make? (e.g. Adding or removing code, refactoring existing code, adding reports)

I completed the all sections for Assignment 2, including ERD, string manipulation, COALESCE, window functions, UNION, CROSS JOIN, INSERT, DELETE, and UPDATE statements.

What did you learn from the changes you have made?

I learned how to use SQL to clean and transform data, handle NULL values, rank and count records with window functions, combine query results with UNION, generate combinations with CROSS JOIN, and modify tables using INSERT, DELETE, ALTER TABLE, and UPDATE.

Was there another approach you were thinking about making? If so, what approach(es) were you thinking of?

Yes. For some queries, I considered using temporary tables or CTEs to break the logic into smaller steps. For the window function questions, I also compared using ROW_NUMBER() versus DENSE_RANK() depending on whether the query returned unique visit dates or all purchase rows.

Were there any challenges? If so, what issue(s) did you face? How did you overcome it?

For the DELETE statement, I initially considered removing the older record by finding the smallest snapshot_timestamp value. However, because the timestamps could be identical when rows were inserted within the same second, I instead used the SQLite rowid to reliably identify and keep the most recently inserted row.

How were these changes tested?

I tested the queries in DB Browser for SQLite by running each query individually and reviewing the output. I checked that filters, rankings, counts, inserted rows, deleted rows, and updated values matched the assignment requirements.

A reference to a related issue in your repository (if applicable)

N/A

Checklist

• I can confirm that my changes are working as intended

[niyazmnazari]

Thank you for submitting assignment 2. All tasks are complete and correct.
Mark: 70/70