|
|
 | | From: | Dawid Kuroczko | | Subject: | Columns into rows. | | Date: | Thu, 13 Jan 2005 11:26:04 +0100 |
|
|
 | I'm working with a quite flat table schema (think: mySQL ;)),
and I want to divide it into two tables.
Lets start with how it looks now:
CREATE TABLE old_table (
id serial PRIMARY KEY,
body text,
path_a varchar(1024),
gendate_a date,
path_bb varchar(1024),
gendate_bb date,
path_ccc varchar(1024),
gendate_ccc date
);
I want to have:
CREATE TABLE new_table (
id serial PRIMARY KEY,
body text
);
CREATE TABLE new_table_paths (
id integer NOT NULL REFERENCES (new_table),
pathtype NOT NULL varchar(10),
path varchar(1024),
gendate date,
PRIMARY KEY(id,pathtype)
);
....what I'm looking for is how to, most efficiently
write a join between new_table and new_table_paths
so it looks like old_table (for compatibility (for other
people)).
I'm thinking about a trigger on schema-table
(with pathtypes), which would automagically update
view whenever schema-table is updated (new pathtype
(like 'a', 'bb', 'ccc')) is added/removed); but this is
implementation.
Now, for the join.
I can write:
SELECT * FROM (SELECT id, path AS path_a FROM new_table_paths WHERE id
= <> AND pathtype = 'a') AS a NATURAL FULL OUTER JOIN (SELECT id,
path AS path_bb FROM new_table_paths WHERE id = <> AND pathtype =
'bb') AS bb; [ and so on... ]
And its fast; however if I move WHERE id = <> outside selects
(for views), it first "materializes" old layout, and then selects
id... total waste.
SELECT * FROM (SELECT id, path AS path_a FROM new_table_paths WHERE
pathtype = 'a') AS a NATURAL FULL OUTER JOIN (SELECT id, path AS
path_bb FROM new_table_paths WHERE pathtype = 'bb') AS bb WHERE id =
<>;
I wonder if you know other way to write this join so it has good performace?
Once again, I need a SELECT since I want a VIEW. :-)
Regards,
Dawid
---------------------------(end of broadcast)---------------------------
TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
|
|
| | From: | Dawid Kuroczko | | Subject: | Re: Columns into rows. | | Date: | Thu, 13 Jan 2005 11:45:52 +0100 |
|
|
| On Thu, 13 Jan 2005 11:26:04 +0100, Dawid Kuroczko wrote:
> I can write:
>
> SELECT * FROM (SELECT id, path AS path_a FROM new_table_paths WHERE id
> = <> AND pathtype = 'a') AS a NATURAL FULL OUTER JOIN (SELECT id,
> path AS path_bb FROM new_table_paths WHERE id = <> AND pathtype =
> 'bb') AS bb; [ and so on... ]
>
> And its fast; however if I move WHERE id = <> outside selects
> (for views), it first "materializes" old layout, and then selects
> id... total waste.
>
> SELECT * FROM (SELECT id, path AS path_a FROM new_table_paths WHERE
> pathtype = 'a') AS a NATURAL FULL OUTER JOIN (SELECT id, path AS
> path_bb FROM new_table_paths WHERE pathtype = 'bb') AS bb WHERE id =
> <>;
>
> I wonder if you know other way to write this join so it has good performace?
> Once again, I need a SELECT since I want a VIEW. :-)
Hmm, something like a multiple column returning aggregate...
As far as I know it is not possible to create aggregate which
could return more than one column? I'm thinking about
something like this:
SELECT id,r2c_aggregate(pathtype, path) FROM new_table_paths GROUP BY id;
....where r2c_aggregate(..) would be a plpgsql function doing the
pathtype+path --> path_a = path, path_bb = path2, path_ccc = path3
assembly. And it would be quite efficient I guess! :)
Hmm, r2c_aggregate could return array of arrays of pathtype/path pairs,
which could be processed by other function which would convert them
into rows, but this is UGLY(TM). :)
Regards,
Dawid
---------------------------(end of broadcast)---------------------------
TIP 2: you can get off all lists at once with the unregister command
(send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
|
|
| | From: | Dawid Kuroczko | | Subject: | Re: Columns into rows. | | Date: | Thu, 13 Jan 2005 12:31:20 +0100 |
|
|
| On Thu, 13 Jan 2005 11:45:52 +0100, Dawid Kuroczko wrote:
> > SELECT * FROM (SELECT id, path AS path_a FROM new_table_paths WHERE
> > pathtype = 'a') AS a NATURAL FULL OUTER JOIN (SELECT id, path AS
> > path_bb FROM new_table_paths WHERE pathtype = 'bb') AS bb WHERE id =
> > <>;
Part of the problem solved:
CREATE AGGREGATE array_aggregate (basetype = anyelement, sfunc =
array_append, stype = anyarray, initcond = '{}');
SELECT id,array_aggregate(pathtype||'='||path) from new_table_paths group by id;
I.e. have a nice array of type=value pairs.
I have however failed to write a function which would take text[] and
return columns. I tried using RETURN record type, but so far it does
not return
anything useful (just a parenthesis enclosed list of column values).
Any hints?
---------------------------(end of broadcast)---------------------------
TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
|
|
|
