When I using the URLs datasource, an exception is thrown at runtime with a string like db://path in the query string, “Error running query: Accepting only relative URLs to ‘http://xxxx.xxxx’”。Is there any way to support these special characters?

I think the problem is you need to URL encode the special characters in your URL. Your example of db://path would be URL encoded as db%3A%2F%2Fpath.