Hi Nuno,
Am 01.03.2014, 14:36 Uhr, schrieb Nuno de Santos Loureiro  
<nlourei at ualg.pt>:
> In one of them I have 's', 'n', 'nc', or NULL.
> I need to change 's' by 'yes', 'nc' by 'yes', 'n' by 'no' and NULL by  
> 'no'.
In Field Calculator you could use:
CASE WHEN column IN ('s','nc') THEN 'yes' ELSE 'no' END
Best wishes,
Anita
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anitagraser.com