Why do two queries run faster than combined subquery?

I'm running postgres 11 on Azure. If I run this query: select min(pricedate) + interval '2 days' from pjm.rtprices It takes 0.153 sec and has the following explain: "Result (cost=2.19..2.20 rows=1 width=8)" " InitPlan 1 (returns $0)" " -> Limit (cost=0.56..2.19 rows=1 width=4)" " -> Index Only Scan using rtprices_pkey on rtprices (cost=0.56..103248504.36 rows=63502562 width=4)" " Index Cond: (pricedate IS NOT NULL)" If I run this query: select pricedate, hour, last_updated, count(1) as N from pjm.rtprices where pricedate Sort (cost=738576.82..739570.68 rows=397541 width=16)" " Sort Key: pricedate DESC, hour, last_updated" " -> Index Scan using rtprices_pkey on rtprices (cost=0.56..694807.03 rows=397541 width=16)" " Index Cond: (pricedate Result (cost=2.19..2.20 rows=1 width=8)" " InitPlan 1 (returns $0)" " -> Limit (cost=0.56..2.19 rows=1 width=4)" " -> Index Only Scan using rtprices_pkey on rtprices rtprices_1 (cost=0.56..103683459.22 rows=63730959 width=4)" " Index Cond: (pricedate IS NOT NULL)" " -> Gather Merge (cost=3791454.84..4662729.67 rows=6316230 width=24)" " Workers Planned: 2" " Params Evaluated: $1" " -> Partial GroupAggregate (cost=3790454.81..3932679.99 rows=3158115 width=24)" " Group Key: rtprices.pricedate, rtprices.hour, rtprices.last_updated" " -> Sort (cost=3790454.81..3812583.62 rows=8851522 width=16)" " Sort Key: rtprices.pricedate DESC, rtprices.hour, rtprices.last_updated" " -> Parallel Seq Scan on rtprices (cost=0.00..2466553.08 rows=8851522 width=16)" " Filter: (pricedate Limit (cost=0.56..1629038.11 rows=3 width=4)" " -> Result (cost=0.56..105887441.26 rows=195 width=4)" " -> Unique (cost=0.56..105887441.26 rows=195 width=4)" " -> Index Only Scan using rtprices_pkey on rtprices rtprices_1 (cost=0.56..105725202.47 rows=64895517 width=4)" " -> Sort (cost=648411.43..649243.43 rows=332798 width=16)" " Sort Key: rtprices.pricedate DESC, rtprices.hour, rtprices.last_updated" " -> Nested Loop (cost=0.56..612199.22 rows=332798 width=16)" " -> CTE Scan on lastday (cost=0.00..0.06 rows=3 width=4)" " -> Index Scan using rtprices_pkey on rtprices (cost=0.56..202957.06 rows=110933 width=16)" " Index Cond: ((pricedate <= lastday.pricedate) AND (pricedate = lastday.pricedate))" This last one is all well and good but if my subquery wasn't extensible to this hack, is there a better way for my subquery to have similar performance to the one at a time approach?