Re: New CORRESPONDING clause design

Hi

I am sending a review of this interesting feature.

I found following issues, questions:

1. unclosed tags <optional> in documentation
2. bad name "changeTargetEntry" - should be makeTargetEntry?
3. Why you removed lot of asserts in prepunion.c? These asserts should be
valid still
4. make_coresponding_target has wrong formatting
5. error "%s queries with a CORRESPONDING clause must have at least one
column with the same name" has wrong formatting, you can show position
6. previous issue is repeated - look on formatting ereport function,
please, you can use DETAIL and HINT fields
7. corresponding clause should to contain column list (I am looking to
ANSI/SQL 99) - you are using expr_list, what has not sense and probably it
has impact on all implementation.
8. typo orderCorrespondingLsit(List *targetlist)
9. I miss more tests for CORRESPONDING BY
10. if I understand to this feature, this query should to work

postgres=# SELECT 1 a, 2 b, 3 c UNION CORRESPONDING BY (c,b) SELECT 4
a, 5 b, 6 c, 8 d;
ERROR: each UNION query must have the same number of columns
LINE 1: ...1 a, 2 b, 3 c UNION CORRESPONDING BY (c,b) SELECT 4 a, 5 b, ...

postgres=# create table t1(a int, b int, c int);
CREATE TABLE
Time: 63,260 ms
postgres=# create table t2(a int, b int);
CREATE TABLE
Time: 57,120 ms
postgres=# select * from t1 union corresponding select * from t2;
ERROR: each UNION query must have the same number of columns
LINE 1: select * from t1 union corresponding select * from t2;

If it is your first patch to Postgres, then it is perfect work!

The @7 is probably most significant - I dislike a expression list there.
name_list should be better there.

Regards

Pavel