Thanks for these adjustments.

But I have some concerns. There should be a better way than specifying a hard-coded font size (it should generally follow the size specified in the desktop environment).

It's also surprising that the behaviour isn't the same in my environment (Ubuntu 18.04, Qt 5.9.5). This is how it looks before this patch:

The only problem being that it is too wide (it overlaps the Ubuntu side icon panel and doesn't get any maximize button). No problem with truncated texts in any button. The dock width cannot grow nor shrink.

And this is after the patch:

The total width is now better, but reducing the font of the buttons in the Edit Database Cell dock is useless (the dock has the same width as before while there is plenty of unused space in the button area).

There should be better ways to accomodate the different text lengths.

For the buttons in Edit Database Cell dock, we could try moving the Set to NULL button to the lower part, at the left of the Apply button.