On Wed, May 31, 2017 at 6:53 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Alexander Korotkov <a.korotkov@postgrespro.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;
I completely agree with that.
If no objections, I will write a patch for that.
Please, find it in attached patch.
I decided to forbid referencing columns by numbers for tables, because those numbers could contain gaps. Also, I forbid altering statistics target for non-expression index columns, because it has no effect.
