[Qgis-user] New Labeling: conditional labels

[Andreas Neumann]

 Hi Giuseppe,

 Thanks for your hint with the syntax - it works in my case.

 I think I sort of understand the syntax - at least the > operator and 
 the substr. What I do not understand is why I need the *-1 (multiplier).

 But I think the syntax is far from being intuitive, without some help. 
 Maybe we can come up with a simple solution in the future?

 If we could combine the rule-based renderer approach with the current 
 labeler (with its new query builder), it would be awesome.

 Thanks for your help!

 Andreas

 On Wed, 28 Dec 2011 20:01:43 +0100, Giuseppe Sucameli wrote:
> Hi Andreas,
>
> On Thu, Dec 22, 2011 at 2:31 PM, Andreas Neumann 
> <a.neumann at carto.net> wrote:
>> What I want is that a label is only drawn if a column value is 
>> larger than
>> 0. I don't want to label features with a value of zero.
>>
>> Do you have any hints how the syntax works for such a case? I see 
>> ">"
>> operators but no "if" or "when".
>
> there's no "if" operator, but ">" returns 1 if true and 0 if false,
> e.g. (field > 5)*10 let's give you 10 or 0 as result.
>
> The problem is that you don't want to display anything when
> the field value is 0, so we can use the substr function.
>
> Here's the solution to your problem:
> substr(id, 0, (id > 0)*-1)
> that means if id <= 0 then substr(id, 0, 0) else substr(id, 0, -1)
>
> In general:
> substr(output, 0, (condition)*-1)
>
> Cheers.
>
>> If it is not possible, then I can still do it in Postgis, but it 
>> would be
>> nice being able to do this in QGIS.
>>
>> Thanks for any hints,
>> Andreas
>>
>> --
>> --
>> Andreas Neumann
>> Böschacherstrasse 10A
>> 8624 Grüt (Gossau ZH)
>> Switzerland
>> _______________________________________________
>> Qgis-user mailing list
>> Qgis-user at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/qgis-user

-- 
 --
 Andreas Neumann
 Böschacherstrasse 10A
 8624 Grüt (Gossau ZH)
 Switzerland