doc: Describe better handling of indexes in ALTER TABLE ATTACH PARTITION

When ALTER TABLE ... ATTACH PARTITION matches partition indexes to the
parent table's indexes, invalid indexes are skipped.  This commit
improves the documentation to describe what e90e9275f56 has changed:
invalid indexes are skipped, and only valid indexes are considered for a
match.

Author: Mohamed Ali <moali.pg@gmail.com>
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/CAGnOmWpAMaE-BOkpwM6mJnHcpS2QZ8yLSSaqmz+vryEsbCWWWA@mail.gmail.com
Backpatch-through: 14

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index dec34337d1ac10fdae9f2f14d06c1dd24cb0b9be..4ca91f81d3439eb8a457aa3e33d592361f42dbf1 100644 (file)
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -1054,10 +1054,11 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       as a partition of the target table. The table can be attached
       as a partition for specific values using <literal>FOR VALUES</literal>
       or as a default partition by using <literal>DEFAULT</literal>.
-      For each index in the target table, a corresponding
-      one will be created in the attached table; or, if an equivalent
-      index already exists, it will be attached to the target table's index,
-      as if <command>ALTER INDEX ATTACH PARTITION</command> had been executed.
+      For each index in the target table, if a valid equivalent index
+      already exists in the partition, it will be attached to the target
+      table's index, as if ALTER INDEX ATTACH PARTITION had been executed;
+      otherwise, a new corresponding index will be created.  Invalid indexes
+      on the partition are skipped.
       Note that if the existing table is a foreign table, it is currently not
       allowed to attach the table as a partition of the target table if there
       are <literal>UNIQUE</literal> indexes on the target table.  (See also