P.S. What's worse, I should have mentioned that the plan *with* indexes
seems flawed:
Create Table t1(f1 int);
Create Table t1(f1 int, f2 int);
Create Unique Index t2f1 on t2(f1);
Create Unique Index t2f2 on t2(f2);
explain update t1 set f1 = Coalesce( (select f2 from t2 x where x.f1 =
t1.f1), t1.f1);
NOTICE: QUERY PLAN:
Seq Scan on t1 (cost=0.00..20.00 rows=1000 width=10) SubPlan -> Index Scan using t2f1 on t2 x (cost=0.00..8.14
rows=10width=4) -> Seq Scan on t2 x (cost=0.00..22.50 rows=1000 width=4)
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