Re: Incorrect cost for MergeAppend

Hi,

> Here is a small patch that reproduces the problem on two tables with
> inheritance, and fixes it. I'll add it to the Commitfest.

Thanks for the patch.

I can confirm that it changes the plan from Sort + Append to MergeAppend.

Before:

```
explain (costs off) select * from ma0 where a < 1000 order by a;
QUERY PLAN
---------------------------------------------------------
Sort
Sort Key: ma0.a
-> Append
-> Index Only Scan using ma0_pkey on ma0 ma0_1
Index Cond: (a < 1000)
-> Seq Scan on ma1 ma0_2
Filter: (a < 1000)
```

After:

```
=# explain (costs off) select * from ma0 where a < 1000 order by a;
QUERY PLAN
---------------------------------------------------
Merge Append
Sort Key: ma0.a
-> Index Only Scan using ma0_pkey on ma0 ma0_1
Index Cond: (a < 1000)
-> Sort
Sort Key: ma0_2.a
-> Seq Scan on ma1 ma0_2
Filter: (a < 1000)
```

The rest of the tests pass.

--
Best regards,
Aleksander Alekseev