It's so you can't define two billings for the same period (say, the same month). To prevent you from double-billing someone. && is the range operator that chec

It's so you can't define two billings for the same period (say, the same month). To prevent you from double-billing someone. && is the range operator that checks for overlap.[1] You have to use gist indexes to do this. And in fact this page doesn't mention it but you have to enable the btree_gist extension with: CREATE EXTENSION btree_gist; before the snippet above will work. [1]: https://www.postgresql.org/docs/current/static/functions-range.html#RANGE-OPERATORS-TABLE https://www.postgresql.org/docs/current/static/functions-ran...