Re: Virtual generated columns

jian he <jian.universality@gmail.com>

From: jian he <jian.universality@gmail.com>

To: Peter Eisentraut <peter@eisentraut.org>

Cc: pgsql-hackers <pgsql-hackers@postgresql.org>

Date: 2024-07-22T08:01:45Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Expand virtual generated columns for ALTER COLUMN TYPE
- 5069fef1cfae 18.0 landed
Eliminate code duplication in replace_rte_variables callbacks
- 363a6e8c6fcf 18.0 landed
Expand virtual generated columns in the planner
- 1e4351af329f 18.0 landed
Virtual generated columns
- 83ea6c54025b 18.0 landed
Additional tests for stored generated columns
- 41084409f635 18.0 landed
Improve generated_stored test
- 44b61efb7928 18.0 landed
- 86749ea3b766 18.0 landed
Fix handling of CREATE DOMAIN with GENERATED constraint syntax
- 84a67725cd11 18.0 landed
Add pg_constraint rows for not-null constraints
- 14e87ffa5c54 18.0 cited
Put generated_stored test objects in a schema
- 894be11adfa6 18.0 landed
Rename regress test generated to generated_stored
- b9ed4969250d 18.0 landed
Small code simplification
- 7ff9afbbd1df 18.0 landed
Remove useless code
- e26d313bad92 18.0 landed
Remove useless initializations
- da2aeba8f533 18.0 landed
doc: Clarify that pg_attrdef also stores generation expressions
- da486d360103 18.0 landed
Clean out column-level pg_init_privs entries when dropping tables.
- 76618097a6c0 17.0 cited
Re-implement the ereport() macro using __VA_ARGS__.
- e3a87b4991cc 13.0 cited

statistic related bug.
borrow examples from
https://www.postgresql.org/docs/current/sql-createstatistics.html

CREATE TABLE t3 (a   timestamp PRIMARY KEY, b timestamp GENERATED
ALWAYS AS (a) VIRTUAL);
CREATE STATISTICS s3 (ndistinct) ON b FROM t3;
INSERT INTO t3(a) SELECT i FROM generate_series('2020-01-01'::timestamp,
                                             '2020-12-31'::timestamp,
                                             '1 minute'::interval) s(i);
ANALYZE t3;
CREATE STATISTICS s3 (ndistinct) ON date_trunc('month', a),
date_trunc('day', b) FROM t3;
ANALYZE t3;
ERROR:  unexpected virtual generated column reference



--this is allowed
CREATE STATISTICS s5 ON (b + interval '1 day') FROM t3;
--this is not allowed. seems inconsistent?
CREATE STATISTICS s6 ON (b ) FROM t3;


in CreateStatistics(CreateStatsStmt *stmt)
we have

if (selem->name)
{
            if (attForm->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("statistics creation on virtual
generated columns is not supported")));
}
else if (IsA(selem->expr, Var)) /* column reference in parens */
{
            if (get_attgenerated(relid, var->varattno) ==
ATTRIBUTE_GENERATED_VIRTUAL)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("statistics creation on virtual
generated columns is not supported")));
}
else                    /* expression */
{
...
}

you didn't make sure the last "else" branch is not related to virtual
generated columns