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

[Daniel Grum]

P Kishor schrieb:
> 2009/10/12 Daniel Grum <daniel.grum at unibw.de>:
>   
>> Hi, I have a probleme with PostgreSQL and PostGIS.
>>
>> I need loops for the programming of a PostGIS SQL-script but PostgreSQL
>>  makes truble.
>>
>> I think I know how I have to use loops in SQL.-->I need loops to update my
>> table line by line!
>>
>> ELSE PostgreSQl said: "as an expression used underinquiry proved more than
>> one line"
>>
>> 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!
>>     
>
> I am not sure what you are trying to do, but you are mixing metaphors
> above. An UPDATE statement is made of
>
> UPDATE <table>
> SET <column_1> = ?, <column_2> = ?, .. <column_n> = ?
> WHERE <condition>
>
> If you update expression is a SELECT statement (a sub-select) then it
> has to return one and only one value. So, the following
>
> 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
>
> won't work because it is likely to return more than one values. Think
> of it this way... you can SET the_geom equal to only one geometry, no?
> So, your sub-select has to return only one geometry.
>
> Perhaps if you explained more clearly what you wanted to do, you would
> get better help.
>
>
>
>
>
>
>   
>> If there are some ideas please help me!
>>
>> --daniel
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>>
>>     
>
>
>
>   
I know that an UPDATE updates the info of one column-->that is the problem.

I only want to save the new information line by line. the geom and the 
distance of one linestring while be changed round by round and this 
changed information should be saved in the table round by round.

So I need a possiblity to save the changed information of the first 
linestring in the first line and in the next lines the informations of 
the changed other linestrings(line by line).

Do you understand what I mean.

--daniel