[postgis-users] Storing geometries in variables

[Shaozhong SHI]

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 <
stephenwoodbridge37 at gmail.com> 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, <ruvenml at beamerbrooks.com
> > <mailto:ruvenml at beamerbrooks.com>> 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, <ruvenml at beamerbrooks.com
> >>     <mailto:ruvenml at beamerbrooks.com>> 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
> >>>
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