Re: ALTER INDEX .. SET STATISTICS ... behaviour

Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> writes:
> I've discovered that PostgreSQL is able to run following kind of queries in
> order to change statistic-gathering target for an indexed expression.

> ALTER INDEX index_name ALTER COLUMN expr SET STATISTICS stat_target;

> It's been previously discussed in [1].

> I think this should be fixed not just in docs. This is why I've started
> thread in pgsql-hackers. For me usage of internal column names "expr",
> "expr1", "expr2" etc. looks weird. And I think we should replace it with a
> better syntax. What do you think about these options?

> ALTER INDEX index_name ALTER EXPRESSION 0 SET STATISTICS stat_target; --
> Refer expression by its number
> ALTER INDEX index_name ALTER EXPRESSION (x + y) SET STATISTICS stat_target;
> -- Refer expression by its definition

Don't like either of those particularly, but what about just targeting
a column by column number, independently of whether it's an expression?

ALTER INDEX myindex ALTER COLUMN 4 SET STATISTICS 1000;

regards, tom lane