How can I perform a unified search on multiple columns, in multiple tables, in multiple databases?

To conduct this kind of search, typically you collect the search terms from the user and issue searches against each source you select. You should conduct the search in parallel by opening a separate connection to each data source on the client and issuing your search. Then the client-side search logic collates, ranks, and passes back the information to the user's UI. The only other technique for carrying out a unified search is to build up a table with data from each source overnight so that the data is ready for online searching the next day. However, this method duplicates the data, which might be a problem when you have space constraints.