Обсуждение: pgsql: doc: move ROW IS NULL examples to a different chapter

doc:  move ROW IS NULL examples to a different chapter

Also add examples.

Reported-by: Wolfgang Walther

Discussion: https://postgr.es/m/21ff8e9c-627a-f949-fb00-a41b9ddcc9d3@technowledgy.de

Backpatch-through: master

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bd86407892126d8c950dd90e6016ea6d0450bd19

Modified Files
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doc/src/sgml/func.sgml   | 14 +++++++++++++-
doc/src/sgml/syntax.sgml | 17 ++++++-----------
2 files changed, 19 insertions(+), 12 deletions(-)