Tender Wang <tndrwang@gmail.com> writes: > generateClonedExtStatsStmt just copy t0's ext_stat info to t1.
So this is a complete mess. The fundamental problem is that transformTableLikeClause believes it can process LIKE_STATISTICS requests immediately, because:
* We may copy extended statistics if requested, since the representation * of CreateStatsStmt doesn't depend on column numbers.
The above comments in transformTableLikeClause and below comments in
generateClonedExtStatsStmt:
* Now handle expressions, if there are any. The order (with respect to * regular attributes) does not really matter for extended stats, so we
* simply append them after simple column references.
now should do some revise.
That was true apparently in the original, limited implementation where we only supported CREATE STATISTICS on plain columns. It's completely wrong for statistics on expressions. IMO what we need to do is make LIKE_STATISTICS work more like LIKE_INDEXES: postpone the transformation until expandTableLikeClause when we know the mapping from source columns to destination columns, and have a chance at converting the expression trees properly, comparably to generateClonedIndexStmt.
> Right now, there is nothing to do in transformExtendedStatistics. > Can we update the varattno to the right value here?
We don't know the column mapping there, either. What we need to have our hands on is the "attmap" computed in expandTableLikeClause, and then we can pass the stats expressions through map_variable_attnos().
This fix looks better than what I said in transformExtendedStatistics.
I think this might not need to be a really large patch, but it definitely has to change where generateClonedExtStatsStmt is called from. I can have a go at it if Tomas doesn't want to.