Likely to be safe, you'd just include both. The problem is that the query planner makes use of equivalence classes to deduce equivalence in quals. If you have a query such as: select * from t1 inner join t2 on t1.x = t2.y where t1.x = 3; then the planner can deduce that t2.y must also be 3 and that qual can be pushed down to the scan level. If t2.y = 3 is quite selective and there's an index on that column, then this deduction is likely going to be a very good win, as the alternative of not using it requires looking at all rows in t2.
Does equivalency only work for constants as in the sample you provided or will it also be found in b1."number" and t0."block_number" in my sample query?
Meaning the columns could be used interchangeably in all the WHERE clauses and the ORDER clause, then it is a matter of figuring out what costs less.
