[postgis-users] IF, ELSE, FOR and WHILE in postgis

[Maxime van Noppen]

Daniel Grum wrote:
> The SQL-Skript:
> UPDATE einheiten_und_bewegungen
> SET the_geom = (SELECT
> ST_Line_SubString(ST_LineMerge(line.the_geom),(1-((Length(line.the_geom)-1000)
> 
>            /Length(line.the_geom))),1)
>        FROM public.einheiten_und_bewegungen line
>        WHERE length(line.the_geom)>1000
>        ORDER BY line.gid);
> 
> In the table einheiten_und_bewegungen are more than one line!

Hi,

It seems that the problem of your query is that the SELECT query might
return more than a row. I thinked what you wanted to write is something
more like :

> UPDATE einheiten_und_bewegungen
> SET the_geom = ST_Line_SubString(ST_LineMerge(the_geom),(1-((Length(the_geom)-1000)/Length(the_geom))),1)
> WHERE length(the_geom)>1000;

I don't see why the select is necessary. This UPDATE query will update
any row where the length of the_geom is >1000 with the formula you provided.

-- 
Maxime