Brug af If-tilstand i where-klausul

select * from sampleTable
where 
  case when @taxtype = 'P' then
    (taxtype = 'P' or  (taxtype = 'E' and code in ('MER','SER')))
  Else
    (taxtype = 'E' and code not in ('MER','SER'))
  end

Ser ud dette vil fungere med Postres

Rediger:

Forlader mit oprindelige svar, fordi hovedindholdet virker, men Postgres har ikke et koncept med variabler ligesom andre RDBMS'er, så jeg omskrev dette som

WITH myconstants as (SELECT 'P'::text as vtaxtype)

select * from sampleTable
where 
  case when (select vTaxType from myconstants) = 'P' then
    (taxtype = 'P' or  (taxtype = 'E' and code in ('MER','SER')))
  Else
    (taxtype = 'E' and code not in ('MER','SER'))
  end;

Her er en SQL Fiddle viser det