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I'm trying to set up some kind of constraint so that I can only enter values in "Table A", if that value exists in "Table B".

I want this to act sort of like a selection list, where there are only a few values that exist in "Table B", which then restricts the values that can be entered into "Table A". (Kind of like a drop down list/ selection list)

I'm using pgAdmin 4 to access a PostGIS DB