[postgis-users] MakeLine into new layer

[Shane Carey]

I figured it out - thanks for your help. I just needed to add the id. Here
is the code:

INSERT INTO long_lines(id, geom) VALUES (1,(
SELECT
   ST_MakeLine(St_LongestLine(
    (SELECT geom FROM floodplainw
    WHERE id = 1),
    (SELECT geom FROM floodplainw
    WHERE id = 1))
)));

Thanks
Le gach dea ghui,
*Shane Carey*
*GIS and Data Solutions Consultant*


On Tue, Oct 23, 2018 at 2:29 PM Shane Carey <careyshan at gmail.com> wrote:

> Thanks Brent, but it keeps returning a error message:
>
> ERROR: column "id" does not exist LINE 2: SELECT id, ^ HINT: There is a
> column named "id" in table "long_lines", but it cannot be referenced from
> this part of the query. SQL state: 42703 Character: 31
>
> Thanks
> Le gach dea ghui,
> *Shane Carey*
> *GIS and Data Solutions Consultant*
>
>
> On Mon, Oct 22, 2018 at 8:26 PM Brent Wood <pcreso at yahoo.com> wrote:
>
>>
>> Off the top of my head...
>> That returns the longest straight line within a polygon.
>>
>> I suggest your workflow is to create a target table first (with a column
>> for the id of the polygon it came from), so you have somewhere to put the
>> linestrings (not necessary, but I find it tidier).
>>
>> eg:
>>
>> *create table long_lines (id integer primary key), geom
>> geometry(LINESTRING, <SRID>);*
>>
>> then run your query...
>>
>> *INSERT INTO long_lines*
>>
>>
>>
>>
>>
>> *SELECT id,     ST_MakeLine(St_LongestLine(    (SELECT geom FROM
>> floodplainw    WHERE id = 1),    (SELECT geom FROM floodplainw    WHERE id
>> = 1))*
>> *); *
>>
>>
>> Cheers
>>
>> Brent Wood
>>
>> ------------------------------
>> *From:* Shane Carey <careyshan at gmail.com>
>> *To:* postgis-users at lists.osgeo.org
>> *Sent:* Tuesday, October 23, 2018 8:07 AM
>> *Subject:* [postgis-users] MakeLine into new layer
>>
>> Hi,
>> I am trying to find the longest line of a polygon and insert it into a
>> new line. I can create the makeline as in the code below but cannot create
>> a new layer out of it using the INTO keyword. Any help would be
>> appreciated. Thanks
>>
>> SELECT
>>    ST_MakeLine(St_LongestLine(
>>     (SELECT geom FROM floodplainw
>>     WHERE id = 1),
>>     (SELECT geom FROM floodplainw
>>     WHERE id = 1))
>> );
>>
>>
>> Le gach dea ghui,
>> *Shane Carey*
>> *GIS and Data Solutions Consultant*
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/postgis-users
>>
>>
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