The years are converted to months and the fractional month is rounded half up:
1.05 year = 12.6 month => 1 year 0.6 month => 1 year 1 month (after rounding)
Compare that to 12.5 months to see when the rounding occurs:
12.5 month / 12 month => 1.0416... years
Plug 1.0416 and 1.0417 into the interval to observe the rounding:
=# select '1.0416 year'::interval, '1.0417 year'::interval; interval | interval ----------+-------------- 1 year | 1 year 1 mon
I understood what you explained, but cannot agree that it's correct.
Run these and you'll see the first and second select are fine, the third ... why ?
select distinct current_date + ((random()::numeric) * '1 year'::interval) from generate_series(1,100) order by 1;
select distinct current_date + ((random()::numeric) * '12 month'::interval) from generate_series(1,100) order by 1; select distinct current_date + ((random()::numeric) || 'year')::interval from generate_series(1,100) order by 1;
So, I have to think ... never use fractional parts on years, right ?
Only to be written, if somebody has to work with fractional parts of years.
This way works
select distinct (random()::numeric) * ('1 year'::interval) from generate_series(1,100) order by 1;
This way doesn´t
select distinct ((random()::numeric) || 'year')::interval from generate_series(1,100) order by 1;