query / filter on attribute tables with external tables joined

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i tried to do some queries on joiend table fields ...

i've got/found some answers concerning version 1.8 - which result in "use select + export to create a combined dataset"so i just did some tests with Layer / query in qgis 2.2 valmiera and 2.3-master(build from 2014-05-02)) and ended up with the same problems:

while

• "layer properties / style / column expression" tool is working finebased on "external" fields - even if i build complex expressions
  
• and "table - select faetures by expressionn" doesn't seem to have any problems with where-clauses
  

"layer / query" returnes strange results with my demo-data; i.e.:

• no problems with expressions unsing fields from the layer's attribute table
  but - as soon as i address "external" fields
• but - as soon as i address "external" fields
  
  • the test feature returns an error:a simple query like "zsp_experimente_xls_WFL01_AREA" >= 1.52"(where 1.52 is valid value out of the sample-list) returns
    "OGR 3 error 1: type mismatch or improper type of arguments to >= operator"
    
    but "zsp_experimente_xls_WOHNFL01_AREA" LIKE "%" returns all records when testing the query ("the where clause teturned 1364 rows")
  • the confusing thing about that:
    the the sample tool privides correct results ! ! !
    ((which means to me that the select part of the statement works fine))

so finally i am still argueing that one of the essential benefits of the join-concept is, that you do not have to mix up geometry and attribute data -> which was a really great idea !!!!!!!

to select data by expression and export geometry and "added" additional data really undermines this concept by duplicating data !!!

so: does anybody have any idea how to deal with that problem ?

best regards robert



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