PALAYRET Jacques <jacques.palayret@xxxxxxxx> writes: > SELECT percentile_cont(1./3) WITHIN GROUP (ORDER BY c1) FROM x ; > percentile_cont > ------------------ > 10.6666666666667 > (1 ligne) > So, I though it should be : > percentile_cont(1./3) = 10.5 (the arithmetic average between 10 et 11) and not 10.6666666666667 As far as I can see from looking at the SQL spec, this is correct; at least, it's clear that we're *not* supposed to just interpolate halfway between the nearest rows. The result is defined to be T0.Y + FACTOR * (T1.Y - T0.Y) where T0.Y and T1.Y are the nearest row values and FACTOR is NVE*(N–1) – floor(NVE*(N–1)) where NVE is the argument of percentile_cont and N is the number of rows. (In SQL:2003, see 10.9 <aggregate function> general rule 7)h)i).) regards, tom lane
