Making banking not fun
26 pages of pain about converting a project from MS SQL to PostgreSQL - one direction only. The document could be useful, if you find yourself stuck in such a situation, but it's also educational if you're interested (as I am) in how compatible different database systems are with each other. Answer: they aren't.
SQL today is in about the state that C was in in the early 1990's: implemented differently by lots of different low-quality vendors. People had to choose, then put up with, a different vendor's combination of features and misfeatures depending on their needs. Then Linux and gcc came along for free and set the bar for competition so high that we hardly remember there used to be a bar (or a market for non-Microsoft C compilers).
SQL today is also similar to 1990's C in that it's the best standard we've got, and the alternative pain we'd be in without it would be truly astonishing.