CASE construct
I've gotten part-way toward implementing a CASE construct in Postgres:
select
case when i = 1 then 10
when i = 2 then 20
end
from t;
(the other parts of the case clause are supported also). But I'm running
into problems in the executor, in that although the query tree seems to
be well-formed, there is not a corresponding plan or plan tree (not sure
of the terminology). Any suggestions on where to start, or interest in
working on it? (hint, hint)
btw, I'm hoping to have a superset of the SQL92 definition; the standard
allows only constants in the "then" clauses afaik, but I'm shooting for
allowing full expressions...
- Tom
I've gotten part-way toward implementing a CASE construct...
... (but) there is not a corresponding plan or plan tree (not sure
of the terminology). Any suggestions on where to start, or interest in
working on it? (hint, hint)
Ah, I've found Bruce's writeup on the query processing dataflow in
tools/backend/index.html.
Looks like a good place to start.
- Tom
I've gotten part-way toward implementing a CASE construct...
... (but) there is not a corresponding plan or plan tree (not sure
of the terminology). Any suggestions on where to start, or interest in
working on it? (hint, hint)Ah, I've found Bruce's writeup on the query processing dataflow in
tools/backend/index.html.Looks like a good place to start.
I was meaning to reply to your first post, but was sick. The way I
usually do it is to look at some feature that already uses it, and copy
that.
For the executor, they are usually spread out in many files.
--
Bruce Momjian | http://www.op.net/~candle
maillist@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026I've gotten part-way toward implementing a CASE construct...
I was meaning to reply to your first post, but was sick. The way I
usually do it is to look at some feature that already uses it, and
copy that.
For the executor, they are usually spread out in many files.
Hope you're feeling better. How scary was the "Bruce-cam" the last few
days? :)
I've concluded that I need to make some fixups in the optimizer to get a
plan which knows about column references inside the CASE clause. In the
meantime, I've got a rudimentary capability with constants:
postgres=> select case
postgres-> when 1 > 2 then 10
postgres-> when 2 > 1 then 20
postgres-> else 30
postgres-> end;
NOTICE: CASE/WHEN not yet implemented
?column?
--------
20
(1 row)
I'm working on matching up types between THEN/ELSE clauses at the parser
stage, but will soon need to get back to trying to figure out the
planner. If I stall out for too long I may just commit the changes to
give someone else a chance to help out (existing features are not
damaged, so it shouldn't hurt).
- Tom
I've gotten part-way toward implementing a CASE construct...
I was meaning to reply to your first post, but was sick. The way I
usually do it is to look at some feature that already uses it, and
copy that.
For the executor, they are usually spread out in many files.Hope you're feeling better. How scary was the "Bruce-cam" the last few
days? :)
Scary. I avoided it. It pops up a window when it is active, so no one
saw the scary-ness.
I've concluded that I need to make some fixups in the optimizer to get a
plan which knows about column references inside the CASE clause. In the
meantime, I've got a rudimentary capability with constants:postgres=> select case
postgres-> when 1 > 2 then 10
postgres-> when 2 > 1 then 20
postgres-> else 30
postgres-> end;
NOTICE: CASE/WHEN not yet implemented
?column?
--------
20
(1 row)
That is interesting.
I'm working on matching up types between THEN/ELSE clauses at the parser
stage, but will soon need to get back to trying to figure out the
planner. If I stall out for too long I may just commit the changes to
give someone else a chance to help out (existing features are not
damaged, so it shouldn't hurt).
Sure. No problem. Advantage of two trees. (See Marc, I am learning.)
--
Bruce Momjian | http://www.op.net/~candle
maillist@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026