[Qgis-user] qgis/postgis : flow map

[Casper Bertelsen]

Try use DB Manager (QGIS Plugin - Comes with standard installation of 
QGIS), here you can connect to the database and run queries and 
afterwards import the queries into QGIS.

When you've create a link to your database in "Add PostGIS-layers" (Ctrl 
+ Shift + D) it should show up in DB manager :) Here it'll be able to 
read the postgis-functions in the database.

Hope it helps.

Mvh. / Best regards
Casper Bertelsen

Mail: casperbj94 at gmail.com

On 03-02-2018 14:06, image wrote:
> Good morning,
>
> I have to do flow map (home->working place) for my area of interest (28
> french cities).
> I get a database .dbf created by a french institute. I imported it into
> postgres/postgis.
> One row = 1 people.
> My table is composed by several fields :
> id (primary key)
> codgeo_res: residence (home) city 's id
> x_resi: residence (home) city 's longitude(centroid)
> y_resi : residence (home) city 's latitude(centroid)
> codgeo_tr : work place city 's id
> x_tr: work city 's longitude(centroid)
> y_tr :work city 's latitude(centroid)
> ipondi : poids de l'individu (weighting value assigned to each individual du
> to the sampling)
> geom : residence (home) city 's ponctual geometry (centroid)
>
>
> So my goal is to create a new table in order 1 row = 1 flow (city A toward
> city B)
> I have to generate useful  geometries (points + lines arrow). Moreover, have
> to apply a SUM on the ipondi field and a GROUP BY on "codgeo_res" field.
>
> Could you throw light for me? Could you help me in order to translate this
> objective to functional sql queries?
>
> Up to now, i tried to run this query throw qgis interface called "virtual
> layer creation" :
> ------------------------------------------------------
> Code:
>
> select
> st_makeline(st_makepoint(entrants_only.x_resi,entrants_only.y_resi),st_makepoint(entrants_only.x_tr,entrants_only.y_tr))as
> geometry,sum(entrants_only.ipondi) as sumipondi, entrants_only.codgeo_res as
> codgeo_res, entrants.codgeo_tr as codgeo_tr
>
> from entrants_only
> group by entrants_only.codgeo_res
> --------------------------------------------------------
>
> But i get this error message :
> ---------------------------------------------------------
> query preparation error on PRAGMA table_info(_tview): no such column
> entrants_only.geom
> ---------------------------------------------------------
>
> Moreover, i send you by attachment the Screen shot representing the error
> message.
> <http://osgeo-org.1560.x6.nabble.com/file/t365144/ss_error_message_qgis2.jpg>
>
> In advance, thank you for your help.
>
>
>
>
>
> --
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