Dropdown & view more Data based on selected value

I have a dynamic options dropdown box. That also works so far.

Now I want to display more data under the dropdown based on the selected entry.

A container with interface events/reload and text node {str:rand} works. When changing from the dropdown, a random number is generated.

But how can I display the additional DB fields from the selected entry?

I found a solution. But: How can I use the System SQL Connection in the custom HTML PHP code?