> On 13/10/2022 18:20 CEST Adrian Klaver <adrian.klaver@xxxxxxxxxxx> wrote: > > In trying to answer an SO question I ran across this: > > Postgres version 14.5 > > select 10^(-1 * 18); > ?column? > ---------- > 1e-18 > > select 10^(-1 * 18::numeric); > ?column? > -------------------- > 0.0000000000000000 > > > Same for power: > > select power(10, -18); > power > ------- > 1e-18 > (1 row) > > select power(10, -18::numeric); > power > -------------------- > 0.0000000000000000 > > > Why is the cast throwing off the result? power has two overloads: https://www.postgresql.org/docs/14/functions-math.html#id-1.5.8.9.6.2.2.19.1.1.1 Calling power(numeric, numeric) is what I expect in that case instead of downcasting the exponent argument to double precision, thus losing precision. select pg_typeof(power(10, -18)), pg_typeof(power(10, -18::numeric)); pg_typeof | pg_typeof ------------------+----------- double precision | numeric (1 row) Determining the right function is described in https://www.postgresql.org/docs/14/typeconv-func.html -- Erik
