pgsql: Doc: spell out comparison behaviors for the date/time types.

Doc: spell out comparison behaviors for the date/time types.

The behavior of cross-type comparisons among date/time data types was
not really explained anywhere.  You could probably infer it if you
recognized the applicability of comments elsewhere about datatype
conversions, but it seems worthy of explicit documentation.

Per bug #16797 from Dana Burd.

Discussion: https://postgr.es/m/16797-f264b0b980b53b8b@postgresql.org

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/7ca285cc2b03a30c2a418da9947650642d688e7d

Modified Files
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doc/src/sgml/func.sgml | 15 +++++++++++++++
1 file changed, 15 insertions(+)