Doc: add info about timestamps with fractional-minute UTC offsets.

Our code has supported fractional-minute UTC offsets for ages, but
there was no mention of the possibility in the main docs, and only
a very indirect reference in Appendix B.  Improve that.

Discussion: https://postgr.es/m/162543102827.697.5755498651217979813@wrigleys.postgresql.org

diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index 483263997f14928b34388c33ed75d06ceb96ef73..4512e80368fdd494ff081cad408e5f5123e345cc 100644 (file)
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -1977,19 +1977,27 @@ MINUTE TO SECOND
          
          
           04:05:06.789-8
-          ISO 8601
+          ISO 8601, with time zone as UTC offset
          
          
           04:05:06-08:00
-          ISO 8601
+          ISO 8601, with time zone as UTC offset
          
          
           04:05-08:00
-          ISO 8601
+          ISO 8601, with time zone as UTC offset
          
          
           040506-08
-          ISO 8601
+          ISO 8601, with time zone as UTC offset
+         
+         
+          040506+0730
+          ISO 8601, with fractional-hour time zone as UTC offset
+         
+         
+          040506+07:30:00
+          UTC offset specified to seconds (not allowed in ISO 8601)
          
          
           04:05:06 PST
@@ -2025,17 +2033,21 @@ MINUTE TO SECOND
           PST8PDT
           POSIX-style time zone specification
          
+         
+          -8:00:00
+          UTC offset for PST
+         
          
           -8:00
-          ISO-8601 offset for PST
+          UTC offset for PST (ISO 8601 extended format)
          
          
           -800
-          ISO-8601 offset for PST
+          UTC offset for PST (ISO 8601 basic format)
          
          
           -8
-          ISO-8601 offset for PST
+          UTC offset for PST (ISO 8601 basic format)
          
          
           zulu
@@ -2043,7 +2055,7 @@ MINUTE TO SECOND
          
          
           z
-          Short form of zulu
+          Short form of zulu (also in ISO 8601)
          
         
        
@@ -2393,6 +2405,24 @@ TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+02'
       
      
 
+    
+     In the ISO style, the time zone is always shown as
+     a signed numeric offset from UTC, with positive sign used for zones
+     east of Greenwich.  The offset will be shown
+     as hh (hours only) if it is an integral
+     number of hours, else
+     as hh:mm if it
+     is an integral number of minutes, else as
+     hh:mm:ss.
+     (The third case is not possible with any modern time zone standard,
+     but it can appear when working with timestamps that predate the
+     adoption of standardized time zones.)
+     In the other date styles, the time zone is shown as an alphabetic
+     abbreviation if one is in common use in the current zone.  Otherwise
+     it appears as a signed numeric offset in ISO 8601 basic format
+     (hh or hhmm).
+    
+
     
      The date/time style can be selected by the user using the
      SET datestyle command, the