My thoughts:
- It probably means "go".
- Postgresql also uses g as a statement terminator. Postgresql is older than MySQL so it might have influenced them.
But as I pointed out in my comment to Andriyev's post above, it's actually making the G uppercase that causes the display to be laid out vertically. Lowercase g doesn't have that effect, or if it does then the documentation doesn't mention it. (I don't have a MySQL install handy to try it out.)
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