doc: Clarify COPY FROM WHERE expression restrictions

Commit aa606b9316a disallowed generated columns in COPY FROM WHERE
expressions, and commit 21c69dc73f9 disallowed system columns.
However, the COPY reference page still mentions only the restriction
on subqueries.

Update the documentation to also list generated columns and system
columns as unsupported in COPY FROM WHERE expressions.

Backpatch the generated-column documentation change to all supported
versions. Backpatch the system-column documentation change to v19,
where that restriction was introduced.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Discussion: https://postgr.es/m/CAHGQGwEgxErc54yVOAVWCsr1O=8pgw4oKRPuEQ9mfhkoYGR_XA@mail.gmail.com
Backpatch-through: 14

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index 4706c9a44100c14090ba601c3ec5e77bc88d69f7..b23433b2c411555dc4b5bb8ac6dada94b6a210d8 100644 (file)
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -545,10 +545,11 @@ WHERE <replaceable class="parameter">condition</replaceable>
    </para>
 
    <para>
-    Currently, subqueries are not allowed in <literal>WHERE</literal>
-    expressions, and the evaluation does not see any changes made by the
-    <command>COPY</command> itself (this matters when the expression
-    contains calls to <literal>VOLATILE</literal> functions).
+    Currently, subqueries, system columns, and generated columns are not
+    allowed in <literal>WHERE</literal> expressions, and the evaluation
+    does not see any changes made by the <command>COPY</command> itself
+    (this matters when the expression contains calls to
+    <literal>VOLATILE</literal> functions).
    </para>
 
     </listitem>