Took this MySQL amateur more than an hour of Googling to find out that the reason file upload to a MySQL BLOB in Rails (see p. 362 in "Agile Web Development with Rails) wasn't working was that Rails only works with MySQL BLOBs in MySQL 4 and later. Nothing ever checks for the MySQL version, the book never mentions this, the Rails site doesn't mention this, that I can see... Just an ugly "Bad SQL syntax" failure.
This wouldn't be a big problem except that some very common Linux distros come with MySQL 3.x by default -- Fedora Core 3 being one of them most relevant to me. Grrrrrr. I hate wasted time.