Just FYI: OpenStreetMap switched from Mysql to PostgreSQL (postgresql), a few years ago.

You mention (link 1):

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# Copyright (C) 2008, 2009, 2010 Gerhard Schwanz
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[download]

and in link 2:

"I want all bridges in the US that are mapped in OpenStreetMap in a PostGIS database"

So, of the two links you gave, one is from before that database switch to postgres, and the other explicitly mentions part of the postgres ecosystem (PostGIS: http://postgis.org/).

No doubt, it is possible to use a database other than postgres but it might be something to be aware of (esp. when using some of the osm tools).