Hi, Steve, I have already read that. I am reading this one now. https://www.postgresql.org/docs/9.0/plpython.html
I find it interesting and intriguing. If a Do statement or a function can also be written in Python, would that imply that highly complex processing can be done this way? Would this add on processing power of Python onto PostgreSQL/PostGIS? I wonder who has experience on this. Regards, Shao On Fri, 21 Aug 2020 at 19:46, Stephen Woodbridge < [email protected]> wrote: > Hi Shao, > > You need to read up on plpgsql stored procedures. This allows you to > write functions that you can call from SQL. Sql is not a programming > language like Python/Perl/Basic/etc, It is a query language for working > with relational databases and operates on sets of records. > > PostgreSQL stored procedures allow you to write and apply functions to > records or columns via the SQL language. This is what PostGIS does. If > you have a table of polygons, you can apply an area calculation to the > polygons in the table of some subset of them like: > > select *, st_area(geom) as area from my_table; > select *, st_area(geom) as area from my_table where gid=1234; > > If you want to write some complex analysis, write a stored procedure and > then apply it like above. plpgsql has flow control, variables, etc like > many other languages. > > -Steve > > On 8/21/2020 2:33 PM, Shaozhong SHI wrote: > > Hi, Ruven Brooks, > > > > I am trying to explore its potential and versatility. > > > > Can standard SQL work like a program? > > > > As I understand, DO statement is similar to a function. > > > > What I am interested in is to fully understand its capabilities and > > working like a program. > > > > Working like to powerful program would allow data manipulation. > > > > Have you tried writing DO statement with Python? > > > > Regards, > > > > Shao > > > > On Fri, 21 Aug 2020 at 18:52, <[email protected] > > <mailto:[email protected]>> wrote: > > > > > > The DO statement is not in standard SQL; it is a PostgreSQL > > extension used to implement procedural languages like PL/SQL. Are > > you writing PL/SQL code? If so, it would be useful to have an > > explanation of what you are trying to compute, particularly if the > > computations are geometric ones. > > > > Ruven Brooks > > > > On 8/21/2020 11:18 AM, Shaozhong SHI wrote: > >> Hi, Ruven Brooks, > >> > >> This is a good point. > >> > >> I was testing in a Do statement. I created a geometry variable. > >> It seems that it stored a geometry object. However, a very long > >> code appeared. It does not seem that the geometry object was not > >> actually stored. > >> > >> Regards, > >> > >> Shao > >> > >> On Fri, 21 Aug 2020 at 15:32, <[email protected] > >> <mailto:[email protected]>> wrote: > >> > >> SQL itself has no variables. What programming language are > >> you using and how does it call SQL? PosgGIS supports WKT > >> format so pretty much any programming language which can > >> store strings can store geometry. > >> > >> Ruven Brooks > >> > >> On 8/21/2020 7:54 AM, Shaozhong SHI wrote: > >>> Has anyone got experience in storing geometries in > >>> variables, so that these can be used in a program? > >>> > >>> Regards, > >>> > >>> Shao > >>> > >>> _______________________________________________ > >>> postgis-users mailing list > >>> [email protected] <mailto: > [email protected]> > >>> https://lists.osgeo.org/mailman/listinfo/postgis-users > >> > >> _______________________________________________ > >> postgis-users mailing list > >> [email protected] > >> <mailto:[email protected]> > >> https://lists.osgeo.org/mailman/listinfo/postgis-users > >> > >> > >> _______________________________________________ > >> postgis-users mailing list > >> [email protected] <mailto: > [email protected]> > >> https://lists.osgeo.org/mailman/listinfo/postgis-users > > > > _______________________________________________ > > postgis-users mailing list > > [email protected] <mailto:[email protected]> > > https://lists.osgeo.org/mailman/listinfo/postgis-users > > > > > > _______________________________________________ > > postgis-users mailing list > > [email protected] > > https://lists.osgeo.org/mailman/listinfo/postgis-users > > _______________________________________________ > postgis-users mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/postgis-users
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