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I want to make a "selection by expression", as shown on the screenshot.

I choose the FIELD and the VALUE from the side panel, but it's selecting 0 rows (there are actually more than 100...).

screen shot

I just don't see why.

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    Make sure you click 'select' in the bottom right corner - the output preview isn't doing the selection for you... – DPSSpatial_BoycottingGISSE Dec 22 '15 at 16:55
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    +1 @mapBaker! This is true, sometimes the Output preview is not a good indication of the result. Always click Select! Let us know if this was the issue so that we can help to find out something else, if not. – wiltomap Dec 22 '15 at 19:34
  • Can you confirm your QGIS version? – ndawson Dec 22 '15 at 20:03
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    Well, I may have hammered the select button, at least I didn't check the result of that thoroughly enough... Indeed it's just working, although the preview still shows 0, or nothing at all. Thanks for your answers! One more question: Select by Expression works more or less the same as a Query Builder? Thanks again – Rob Dec 23 '15 at 10:55
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    Output preview does not show the number of matched features. Expressions in the query builder return True (feature is in the result set) or False (feature is not). I cannot interpret output preview in this case. When using field calculator output preview shows an example of the result, maybe the first? – Detlev Dec 23 '15 at 16:09

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