This query will show you workbook in the left column and the published data source on the right:
data_connections.owner_id = workbooks.id AND
data_connections.dbclass = 'sqlproxy';
The revelatory part here is that "owner_id" in the data_connections table isn't a person... it's a thing. (Maybe the column name made more sense in the past.) Other words, the data_connections.owner_id field refers to the workbook that contains it. (If I recall, it can also refer to a published data source, but since that's not what you're trying to find here, I think it's irrelevant.)
Thanks Rick, yes OWNER_ID threw me off. I really appreciate the guidance!!
You're very welcome!
I just remembered too that I should put a plug for the Workgroups Database Data Dictionary here. It's a great resource for this kind of thing. (Although I had remembered the point of confusion on this column from an earlier bout with the same kind of question.)