Index columns with arithmetic operators

I commonly make this query on my database
SELECT * FROM Example_tab WHERE Column_a + Column_b < 10;.

Is it possible to create indexes based on Column_a + Column_b < 10 to speed up this lookup. I see it is possible to do it for oracle based db over here (by doing CREATE INDEX Idx ON Example_tab(Column_a + Column_b);).But I can’t find it anywhere for postgresql or mysql.

Is it even possible to do it on databases other than oracle ? If yes, is it documented somewhere, what are they called (basically, what should I google to find them) ?

Thanks in advance for any help.