pgsql: doc: Mention validation attempt during ALTER INDEX .. ATTACH PAR

doc: Mention validation attempt during ALTER INDEX .. ATTACH PARTITION

Since 9d3e094f12, the command tries to validate the parent index of the
named index, if invalid. The documentation did not mention this
behavior, which could be confusing.

Author: Mohamed ALi <moali.pg@gmail.com>
Discussion: /messages/by-id/CAGnOmWpHu25_LpT=zv7KtetQhqV1QEZzFYLd_TDyOLu1Od9fpw@mail.gmail.com
Backpatch-through: 14

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/7a24fad3d9f39cfa187b3fd240211c0de7615f9a

Modified Files
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doc/src/sgml/ref/alter_index.sgml | 5 +++++
1 file changed, 5 insertions(+)