[postgis] PostgreSql point to Postgis point conversion

[M Vermeij]

I am trying to use the :

update a set g = geometryfromtext(('POINT(' ||
> x || ' '
> ||y||')')::geometry,123);
 you mentioned. However instead of you're x and y
columns I would like to use the x and y coordinates
which are already stored in a postgres point field,
but can't seem to retrieve them seperately. 

Question:
If the postgres point field is called 'location' what
whould the UPDATE command then be? ('location2' is the
PostGis point field.)

UPDATE table1 set location2 =geometryfromtext(( 
???????    )::geometry,-1);




--- Dave Blasby <dblasby at refractions.net> wrote:
> Here's the easiest way to do it - just use
> postgresql's builtin TEXT
> type to create the WKT:
> 
> t1=# create table a (x float, y float, g geometry);
> 		....
> 
> t1=# select * from a;
>  x  | y  | g 
> ----+----+---
>   1 |  2 | 
>  11 | 22 | 
> (2 rows)
> 
> 
> To make these into points, we make some WKT (|| is
> the concat operator):
> 
> 
> t1=# select 'POINT(' || x || ' ' ||y||')' from a;
>    ?column?   
> --------------
>  POINT(1 2)
>  POINT(11 22)
> (2 rows)
> 
> So, 
> 
> t1=# update a set g = geometryfromtext(('POINT(' ||
> x || ' '
> ||y||')')::geometry,123);
> t1=# select * from a;
>  x  | y  |           g           
> ----+----+-----------------------
>   1 |  2 | SRID=123;POINT(1 2)
>  11 | 22 | SRID=123;POINT(11 22)
> (2 rows)
> 
> 
> dave
> 


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