yaooqinn commented on issue #26418: [SPARK-29783][SQL] Support SQL Standard/ISO_8601 output style for interval type URL: https://github.com/apache/spark/pull/26418#issuecomment-552946152 > We can't change the behavior of multi-unit syntax as it has been there for a long time, and the pgsql behavior is really confusing. yes, so we use the SQL standard for display only. > > AFAIK the SQL standard only allows one leading `-` in the year-month or day-time interval string, which is difficult for us to follow: how can we represent 1 day - 3 hour? ```sql postgres=# set IntervalStyle=sql_standard; SET postgres=# select interval '-1 year -1 day -1 hour'; interval ------------------ -1-0 -1 -1:00:00 (1 row) postgres=# select interval '-1 year 1 day 1 hour'; interval ------------------ -1-0 -1 -1:00:00 (1 row) postgres=# select interval '-1 year 1 day +1 hour'; interval ------------------ -1-0 +1 +1:00:00 (1 row) postgres=# select interval '+1 year 1 day +1 hour'; interval ------------------ +1-0 +1 +1:00:00 (1 row) ``` One proper way is that we add explicit signs for each part to eliminate ambiguity as shown in the above cases. So in that case, `1 day - 3 hour` will be `+1 -3:00:00`.
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