Howto sort the result of UNION (without modifying its type)?

On 04/08/2011 03:44 PM, Clemens Eisserer wrote:

Hi,

I have a query where I UNION several select statements which return
IDs of type INTEGER.
This works well, if the IDs don't need to be sorted:

SELECT id FROM table WHERE id IN ((select id FROM table WHERE ...) UNION (SELECT id FROM table_ WHERE ....))

However I need the result the UNIONs to be sorted, so I tried the following:

SELECT id FROM table WHERE id IN (SELECT col0 FROM ((select id FROM table WHERE ...) UNION (SELECT id FROM table_ WHERE ....)) AS col0 ORDER BY col0 OFFSET X LIMIT Y)

FEHLER: Operator existiert nicht: integer = record
ERROR: Operator does not exist: integer = record
LINE 1: Select id FROM table WHERE id IN (Select col0 FROM ...

Is there any way to get the results of UNIONs sorted, without
converting it to record?

Thanks, Clemens

PS: I know the query looks really stupid, however the queries I UNION
are auto-generated SQL.
I don't have much choice here to write the query more efficient :/

does this work for you?

select u.id from (your unions) as u order by u.id

Hi Robert,

does this work for you?
       select u.id from (your unions) as u order by u.id

Unfourtunatly not, it converts my union-results from INTEGER to RECORD.
However, it seems to be possible to order the unions directly:

result1 UNION result2 ORDER BY u.id

Hmm, the query plan looks really insane for this ... wonder how it
will perform when the tables will not be mostly empty ;)

Thanks, Clemens

Clemens Eisserer <linuxhippy@gmail.com> Friday 08 April 2011 23:44:21

Hi,

I have a query where I UNION several select statements which return
IDs of type INTEGER.

This works well, if the IDs don't need to be sorted:

SELECT id FROM table WHERE id IN ((select id FROM table WHERE ...) UNION
(SELECT id FROM table_ WHERE ....))

However I need the result the UNIONs to be sorted, so I tried the following:

SELECT id FROM table WHERE id IN (SELECT col0 FROM ((select id FROM table
WHERE ...) UNION (SELECT id FROM table_ WHERE ....)) AS col0 ORDER BY
col0 OFFSET X LIMIT Y)

FEHLER: Operator existiert nicht: integer = record
ERROR: Operator does not exist: integer = record
LINE 1: Select id FROM table WHERE id IN (Select col0 FROM ...

Is there any way to get the results of UNIONs sorted, without
converting it to record?

Thanks, Clemens

PS: I know the query looks really stupid, however the queries I UNION
are auto-generated SQL.
I don't have much choice here to write the query more efficient :/

May you try construct like this:
SELECT i FROM (/* Your query example: */ SELECT i from v1 union select i from
v2) as alias order by i;
?

Clemens Eisserer <linuxhippy@gmail.com> Friday 08 April 2011 23:44:21

Hi,

I have a query where I UNION several select statements which return
IDs of type INTEGER.

This works well, if the IDs don't need to be sorted:

SELECT id FROM table WHERE id IN ((select id FROM table WHERE ...) UNION
(SELECT id FROM table_ WHERE ....))

However I need the result the UNIONs to be sorted, so I tried the following:

SELECT id FROM table WHERE id IN (SELECT col0 FROM ((select id FROM table
WHERE ...) UNION (SELECT id FROM table_ WHERE ....)) AS col0 ORDER BY
col0 OFFSET X LIMIT Y)

FEHLER: Operator existiert nicht: integer = record
ERROR: Operator does not exist: integer = record
LINE 1: Select id FROM table WHERE id IN (Select col0 FROM ...

Is there any way to get the results of UNIONs sorted, without
converting it to record?

Thanks, Clemens

PS: I know the query looks really stupid, however the queries I UNION
are auto-generated SQL.
I don't have much choice here to write the query more efficient :/

May you try construct like this:
SELECT i FROM (/* Your query example: */ SELECT i from v1 union select i from
v2) as alias order by i;
?
P.S. Sorry if this message was sent twice.