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<font face="Helvetica, Arial, sans-serif">You're far better off
going the other way. It's really easy to call PostgreSQL/PostGIS
from Python and there are lots of tutorials and examples. The
advantage of doing it this way is you can also use Python for user
interface interaction and graphical data display.<br>
<br>
An alternative to consider if maps are particularly of interest is
to write most of your code in Javascript. PostgresSQL can create
JSON which can be fed directly to Leaflet or Google Maps to
display as maps.<br>
<br>
It turns out that SQL is Turing Complete (without pl/SQL). This
means that any computation you can write in Python or any other
programming language, you can write in SQL. In other words, SQL
is already as powerful as Python. What this claim doesn't say is
how large and long the program will be and how fast it will run.
Unfortunately, that depends on the specific computation and the
answer could go either way. <br>
<br>
The typical usage of pl/SQL and pl/Python are like the one Stephen
Woodbridge gave, writing a function like st_area which takes just
a single column of a single row as input and returns a floating
point value. The postgreSQL query optimizer does not optimize
pl/SQL functions so the programmer must be extremely careful to
write these efficiently. <br>
<br>
Ruven Brooks</font><br>
<div class="moz-cite-prefix">On 8/21/2020 3:00 PM, Shaozhong SHI
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CA+i5JwbnEH-RBFVrCVM5U8YaHJ4yevj6cOeU-W9q0uOGaOzs7g@mail.gmail.com">
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<div dir="ltr">Hi, Steve,
<div><br>
</div>
<div>I have already read that. I am reading this one now. <a
href="https://www.postgresql.org/docs/9.0/plpython.html"
moz-do-not-send="true">https://www.postgresql.org/docs/9.0/plpython.html</a></div>
<div><br>
</div>
<div>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?</div>
<div><br>
</div>
<div>Would this add on processing power of Python onto
PostgreSQL/PostGIS?</div>
<div><br>
</div>
<div>I wonder who has experience on this.</div>
<div><br>
</div>
<div>Regards,</div>
<div><br>
</div>
<div>Shao</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, 21 Aug 2020 at 19:46,
Stephen Woodbridge <<a
href="mailto:stephenwoodbridge37@gmail.com"
moz-do-not-send="true">stephenwoodbridge37@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi
Shao,<br>
<br>
You need to read up on plpgsql stored procedures. This allows
you to <br>
write functions that you can call from SQL. Sql is not a
programming <br>
language like Python/Perl/Basic/etc, It is a query language
for working <br>
with relational databases and operates on sets of records.<br>
<br>
PostgreSQL stored procedures allow you to write and apply
functions to <br>
records or columns via the SQL language. This is what PostGIS
does. If <br>
you have a table of polygons, you can apply an area
calculation to the <br>
polygons in the table of some subset of them like:<br>
<br>
select *, st_area(geom) as area from my_table;<br>
select *, st_area(geom) as area from my_table where gid=1234;<br>
<br>
If you want to write some complex analysis, write a stored
procedure and <br>
then apply it like above. plpgsql has flow control, variables,
etc like <br>
many other languages.<br>
<br>
-Steve<br>
<br>
On 8/21/2020 2:33 PM, Shaozhong SHI wrote:<br>
> Hi, Ruven Brooks,<br>
><br>
> I am trying to explore its potential and versatility.<br>
><br>
> Can standard SQL work like a program?<br>
><br>
> As I understand, DO statement is similar to a function.<br>
><br>
> What I am interested in is to fully understand its
capabilities and <br>
> working like a program.<br>
><br>
> Working like to powerful program would allow data
manipulation.<br>
><br>
> Have you tried writing DO statement with Python?<br>
><br>
> Regards,<br>
><br>
> Shao<br>
><br>
> On Fri, 21 Aug 2020 at 18:52, <<a
href="mailto:ruvenml@beamerbrooks.com" target="_blank"
moz-do-not-send="true">ruvenml@beamerbrooks.com</a> <br>
> <mailto:<a href="mailto:ruvenml@beamerbrooks.com"
target="_blank" moz-do-not-send="true">ruvenml@beamerbrooks.com</a>>>
wrote:<br>
><br>
><br>
> The DO statement is not in standard SQL; it is a
PostgreSQL<br>
> extension used to implement procedural languages like
PL/SQL. Are<br>
> you writing PL/SQL code? If so, it would be useful
to have an<br>
> explanation of what you are trying to compute,
particularly if the<br>
> computations are geometric ones.<br>
><br>
> Ruven Brooks<br>
><br>
> On 8/21/2020 11:18 AM, Shaozhong SHI wrote:<br>
>> Hi, Ruven Brooks,<br>
>><br>
>> This is a good point.<br>
>><br>
>> I was testing in a Do statement. I created a
geometry variable. <br>
>> It seems that it stored a geometry object.
However, a very long<br>
>> code appeared. It does not seem that the
geometry object was not<br>
>> actually stored.<br>
>><br>
>> Regards,<br>
>><br>
>> Shao<br>
>><br>
>> On Fri, 21 Aug 2020 at 15:32, <<a
href="mailto:ruvenml@beamerbrooks.com" target="_blank"
moz-do-not-send="true">ruvenml@beamerbrooks.com</a><br>
>> <mailto:<a
href="mailto:ruvenml@beamerbrooks.com" target="_blank"
moz-do-not-send="true">ruvenml@beamerbrooks.com</a>>>
wrote:<br>
>><br>
>> SQL itself has no variables. What
programming language are<br>
>> you using and how does it call SQL? PosgGIS
supports WKT<br>
>> format so pretty much any programming
language which can<br>
>> store strings can store geometry.<br>
>><br>
>> Ruven Brooks<br>
>><br>
>> On 8/21/2020 7:54 AM, Shaozhong SHI wrote:<br>
>>> Has anyone got experience in storing
geometries in<br>
>>> variables, so that these can be used in a
program?<br>
>>><br>
>>> Regards,<br>
>>><br>
>>> Shao<br>
>>><br>
>>>
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