Deadly sins againts database performance/scalability

Hello,

I'm just creating some document how developers should/must not behave when dealing with Oracle database. I written down some basic rules and came with idea what's the most stupid thing that you can do to your database.
I have two on mind, first one is not using BIND variables and the second one is using COMMIT in a loop statement. However, there will be more of these.
So I have question to you here. What's the most stupid, but in real world foundable, mistakes in development applications using Oracle datatabase?

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with regards

Dusan Bolek