# Exercise: Modifying Data

Add a category, products, yourself and a customer's order to Northwind, then update and delete them, with scripts that use variables and transactions.

Apprentice · T-SQL · SQL · Updated October 30, 2026

Time to change some real data. In this exercise you'll open a new line of business for Northwind Traders: a Sporting Goods category with its own products. You'll hire yourself, take a customer's first order, raise some prices, and finally close the category down again, in nine SQL problems that build on each other.

## Get the exercise files

Open this lesson's GitHub repository, [github.com/ask-codey/exercise-modifying-data](https://github.com/ask-codey/exercise-modifying-data), also linked from the **Exercise** box beside the lesson. Click **Code**, then **Download ZIP**, and unzip it into your `bootcamp` folder.

Start fresh: run `Northwind.sql` from the course's sample databases first, so the examples you tried in the lessons (including their Sporting Goods category) are gone.

Each `.sql` file holds one problem as a comment. Open it in SSMS (**File > Open > File...**), choose **Northwind** in the database drop-down, and write your SQL under the problem. Then select it (with the `DECLARE` lines at the top, in problems 5, 7 and 9) and press **F5**.

| File | You'll practice |
|---|---|
| `01_Insert_Category.sql` | `INSERT` |
| `02_Find_Category_Id.sql` | finding a new row's identity value |
| `03_Insert_Products.sql` | inserting several rows, with a variable |
| `04_Add_Yourself.sql` | an `INSERT` with dates and empty columns |
| `05_New_Customer_With_Order.sql` | a script with variables and a transaction |
| `06_Update_Hire_Date.sql` | `UPDATE` |
| `07_Raise_Category_Prices.sql` | a calculated `UPDATE`, driven by variables |
| `08_Delete_Product.sql` | `DELETE` |
| `09_Delete_Category.sql` | deleting in the order the foreign keys allow |

## Check your work

There are no tests for SQL here: you check your own work, the way you would on the job.

- Each problem says what to expect, such as `(5 rows affected)`. Compare it with the **Messages** tab.
- After each change, run a `SELECT` and look at the data.
- Before every `UPDATE` and `DELETE`, run a `SELECT` with the same `WHERE` first.

## Hints

- **Look things up; don't type ids.** `SELECT @CategoryId = CategoryId FROM Categories WHERE CategoryName = 'Sporting Goods';` puts a row's value into a variable.
- **An INSERT can take its rows from a SELECT.** `INSERT INTO OrderDetails (...) SELECT ... FROM Products WHERE ...` inserts one row for each product the `SELECT` finds. It's handy in problem 5.
- **Dates:** `GETDATE()` is now, and `DATEADD(day, -14, GETDATE())` is two weeks ago.
- **Read the error in problem 9.** It tells you exactly which table still points at the category.

## Starting over

If something goes wrong, run `Northwind.sql` from the course's sample databases again. It creates Northwind fresh, and you can start from problem 1.

## Submit your exercise

The exercise is how you finish this lesson. When your work is done, put it on GitHub in a repo of your own, then submit that repo's address here.

1. On GitHub, click **+**, then **New repository**. Name it (for example `exercise-modifying-data`), choose **Public**, and click **Create repository**. Leave out the README: your folder already has one.
2. In a terminal in your exercise folder (Git Bash on Windows), send your work to your new repo. If you downloaded the ZIP:

   ```bash
   git init -b main
   git add .
   git commit -m "My solution"
   git remote add origin https://github.com/your-name/exercise-modifying-data.git
   git push -u origin main
   ```

   If you cloned the starter instead, point your copy at your own repo, then commit and push:

   ```bash
   git remote set-url origin https://github.com/your-name/exercise-modifying-data.git
   git add .
   git commit -m "My solution"
   git push -u origin main
   ```

3. Paste your repo's address, such as `https://github.com/your-name/exercise-modifying-data`, into **Submit your exercise** on this page. The site checks that the repo is public and holds your commits, and then the lesson is complete.

Changed something after you submitted? Push it, and submit again: your latest submission is the one that counts.

## So what

Insert, update and delete, with variables, lookups and transactions, is the work behind every Save button. You've just done it by hand; soon your C# code will do it for you.

## Key terms

- [INSERT](https://www.ask-codey.com/glossary/insert)
- [UPDATE](https://www.ask-codey.com/glossary/update)
- [DELETE](https://www.ask-codey.com/glossary/delete)
- [Transaction](https://www.ask-codey.com/glossary/transaction)

## Related

- [Inserting Data](https://www.ask-codey.com/lessons/modifying-data-in-t-sql-inserting-data)
- [Updating Data](https://www.ask-codey.com/lessons/modifying-data-in-t-sql-updating-data)
- [Deleting Data](https://www.ask-codey.com/lessons/modifying-data-in-t-sql-deleting-data)
- [Transactions](https://www.ask-codey.com/lessons/modifying-data-in-t-sql-transactions)

Source: https://www.ask-codey.com/lessons/exercise-modifying-data