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

I created SQL scripts for selct, inserting, updating, and deleting records safely, and added logic for tracking product quantities.

What did you learn from the changes you have made?

I learned how to use COALESCE to handle NULL values, ensure safe INSERT/DELETE operations, and apply subqueries inside UPDATE and SELECT statements.

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

Yes, I considered using joins for the update and finding the latest quentity instead of correlated subqueries, but chose the subquery for simplicity.

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

How were these changes tested?

I ran queries on sample data, verified the product_units table after each step, and confirmed correct values (nulls replaced with zeros, latest quantities updated)

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

Checklist

• I can confirm that my changes are working as intended