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 8433344e5b6f5eb7f6db8145f73d5493c23a2cee..5413bb0e12d775eff36d111aaac9c62e1ed596d4 100644 (file)
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -480,10 +480,11 @@ 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 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>