pgsql: Allow SET STATISTICS on expression indexes

Allow SET STATISTICS on expression indexes

Index columns are referenced by ordinal number rather than name, e.g.
CREATE INDEX coord_idx ON measured (x, y, (z + t));
ALTER INDEX coord_idx ALTER COLUMN 3 SET STATISTICS 1000;

Incompatibility note for release notes:
\d+ for indexes now also displays Stats Target

Authors: Alexander Korotkov, with contribution by Adrien NAYRAT
Review: Adrien NAYRAT, Simon Riggs
Wordsmith: Simon Riggs

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5b6d13eec72b960eb0f78542199380e49c8583d4

Modified Files
--------------
doc/src/sgml/ref/alter_index.sgml | 39 +++++++++++++++++++++
src/backend/commands/tablecmds.c | 55 +++++++++++++++++++++++-------
src/backend/nodes/copyfuncs.c | 1 +
src/backend/nodes/equalfuncs.c | 1 +
src/backend/parser/gram.y | 16 +++++++++
src/backend/utils/cache/syscache.c | 46 +++++++++++++++++++++++++
src/bin/psql/describe.c | 2 ++
src/bin/psql/tab-complete.c | 5 ++-
src/include/nodes/parsenodes.h | 2 ++
src/include/utils/syscache.h | 3 ++
src/test/regress/expected/alter_table.out | 24 +++++++++++++
src/test/regress/expected/create_index.out | 8 ++---
src/test/regress/sql/alter_table.sql | 16 +++++++++
13 files changed, 201 insertions(+), 17 deletions(-)