I need to achieve the following functionality for my work, but sort of stuck in the middle.
1. Retrieve data from a table based on some condition
2. Populate this data onto a drop down list
3. Select a value in the drop down list
4. Use this selected value to query another table to fetch a couple of other rows
5. Using the rows fetched in step 4 to populate another drop down list.

So far I have achieved 1-3, but not very sure how to proceed to 4. Can anyone help out, please?