Re: support create index on virtual generated column.

Hi everyone,

While revisiting the discussion for `CF6749 — Disallow whole-row index references with virtual generated columns? `
Based on version V7, I’ve added support for whole-row references within partial indexes, attached V8 patch.

There is one point I may have overlooked: the current implementation appears to only work for btree indexes.

I welcome everyone’s thoughts and look forward to your feedback.

Below are the test results:
-- test creation of a predicate index with a whole-row expression
DROP TABLE IF EXISTS test_pg_wholerow;
NOTICE: table "test_pg_wholerow" does not exist, skipping
CREATE TABLE test_pg_wholerow(a int, b int GENERATED ALWAYS AS (a * 2) VIRTUAL, c text);
CREATE UNIQUE INDEX test_pg_wholerow_pred_idx ON test_pg_wholerow(a) WHERE test_pg_wholerow IS NOT NULL;
INSERT INTO test_pg_wholerow(a,c) SELECT NULL, NULL FROM generate_series(1, 1000);
INSERT INTO test_pg_wholerow(a,c) SELECT 1, '1';
ANALYZE test_pg_wholerow;
SELECT relname,reltuples FROM pg_catalog.pg_class WHERE relname IN ('test_pg_wholerow', 'test_pg_wholerow_pred_idx') ORDER BY OID;
relname | reltuples
---------------------------+-----------
test_pg_wholerow | 1001
test_pg_wholerow_pred_idx | 1
(2 rows)

EXPLAIN (COSTS OFF) SELECT * FROM test_pg_wholerow WHERE test_pg_wholerow IS NOT NULL;
QUERY PLAN
----------------------------------------------------------------
Index Scan using test_pg_wholerow_pred_idx on test_pg_wholerow
(1 row)

EXPLAIN (COSTS OFF) SELECT a FROM test_pg_wholerow WHERE test_pg_wholerow IS NOT NULL;
QUERY PLAN
---------------------------------------------------------------------
Index Only Scan using test_pg_wholerow_pred_idx on test_pg_wholerow
(1 row)

EXPLAIN (COSTS OFF) SELECT a,b FROM test_pg_wholerow WHERE test_pg_wholerow IS NOT NULL;
QUERY PLAN
---------------------------------------------------------------------
Index Only Scan using test_pg_wholerow_pred_idx on test_pg_wholerow
(1 row)

regards,
--
ZizhuanLiu (X-MAN) 
44973863(at)qq(dot)com