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doc: Add note about generated columns in foreign tables

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Explain that it is not enforced that querying a generated column
returns data that is consistent with the data that was stored.  This
is similar to the note about constraints nearby.

Reported-by: Amit Langote <amitlangote09@gmail.com>
This commit is contained in:
Peter Eisentraut 2019-04-08 13:47:46 +02:00
parent 119dcfad98
commit 348f57ce5b
1 changed files with 10 additions and 0 deletions
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doc/src/sgml/ref/create_foreign_table.sgml
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@ -350,6 +350,16 @@ CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ]
reality.
</para>
<para>
Similar considerations apply to generated columns. Stored generated
columns are computed on insert or update on the local
<productname>PostgreSQL</productname> server and handed to the
foreign-data wrapper for writing out to the foreign data store, but it is
not enforced that a query of the foreign table returns values for stored
generated columns that are consistent with the generation expression.
Again, this might result in incorrect query results.
</para>
<para>
While rows can be moved from local partitions to a foreign-table partition
(provided the foreign data wrapper supports tuple routing), they cannot be