Re: Can't use ORDER BY in subqueries

Thanks Stefan, the solution you proposed works out (the one without the function). I used the following to get what I want: SELECT COUNT(*) FROM POLYGONS one JOIN (SELECT LINE FROM LINES where length(line) = (select max(length(line)) from lines) ) two ON "Intersect"(one.polygon, two.line) = TRUE; Leo

On 05 Nov 2014, at 18:31, Stefan Manegold wrote:

in case the ("our") optimizer indeed fails to push-down the selection, maybe giving a hint like this

select count(*) From polygons one join (select line from lines where two.id in (select id from line_max())) two ON "Intersect"(one.polygon,two.line) = TRUE;

or even

with two as (select line from lines where two.id in (select id from line_max())) select count(*) From polygons one join two ON "Intersect"(one.polygon,two.line) = TRUE;

helps?

the (intermediate) result might still be as large as polygons in case the longest lines intersects with all polygons ...

Stefan

----- Original Message -----

...

the pitfall of deciding on how queries executed. given the message it looks like a cartesian product. ;)

On 5 nov. 2014, at 18:01, Leo Kotschenreuther < leo.kotschenreuther@student.hpi.de > wrote:

Hi,

I have two tables: CREATE TABLE lines (ID INT, size INT, line GEOMETRY); CREATE TABLE polygons (ID INT, size INT, polygon GEOMETRY);

The query I want to call is the following: SELECT COUNT(*) FROM POLYGONS one JOIN (SELECT LINE FROM LINES ORDER BY Length(line) DESC LIMIT 1) two ON "Intersect"(one.polygon, two.line) = TRUE;

I tried out to create a function that replaces the use of the subquery: create function line_max() returns table (id integer) begin return select id from lines order by Length(line) desc limit 1; end;

select count(*) From polygons one join lines two ON "Intersect"(one.polygon, two.line) = TRUE where two.id in (select id from line_max());

The query started without errors but it stops with the following error: HEAPalloc: Insufficient space for HEAP of 7200000000 bytes.

Thanks Leo

On 05 Nov 2014, at 17:48, Stefan Manegold < Stefan.Manegold@cwi.nl > wrote:

Hi Leo,

could you give an SQL example of the very query you'd like to run but that MonetDB "rejects" due to order by and/or limit in a sub query?

Thanks!

Stefan

----- Original Message -----

Hi,

I understand why Monetdb does’t support ORDER BY in subqueries.

An ORDER BY combined with a LIMIT does influence the size of the query result set. Is there a workaround to use such a query?

Here’s my use case: I’m working with the spatial extension and have a table filled with polygons. Now I want to know the ids of all polygons that intersect the polygon with the biggest area.

Is there a chance to answer this use case with only one query?

Regards Leo

On 27 Oct 2014, at 19:02, Martin Kersten < Martin.Kersten@cwi.nl > wrote:

Hi

ORDER BY (and LIMIT/OFFSET for that matter) only control the overall shape of the query result set. Hence, they are indeed not supported within subqueries in MonetDB.

See thread https://www.monetdb.org/pipermail/users-list/2013-October/006861.html

regards, Martin

On 27/10/14 17:57, Kotschenreuther, Leo wrote:

Hi all,

I tried to use some more complex queries, they contained subqueries. I will shortly desrcibe the situation:

I have two tables (e.g. test and foo) and want to join them. Furthermore I want to preselect a subset of one of the two tables by adding some conditions (e.g. order the records by attribute c and only choosing the biggest one). A query could look like the this:

*sql>select * from test join (select * from foo order by c limit 1);* * * The result I receive is the following:

*syntax error, unexpected ORDER, expecting INTERSECT or EXCEPT or UNION or ')' in: "select * from test join (select * from foo order**”* * * On the other hand, I can run the subquery without the main query and I receive a valid result.

Is there a possibility to use subqueries with an ORDER BY statement without separating them into two independent queries?

Regards Leo

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