plpgsql related question: intervals and variables

Hello out there,

We have a problem in plpgsql:
We want to add variable periods (result of a query) to a timestamp.

Our Code looks like this:

Begin
  heute := ''today'';
Select Into vk ourcolumn From table where other = foo;  If vk > 0 Thenvk_txt := ''Vorkuehlung notwendig'';        ez
:=heute + interval ''vk days'';       Else     vk_txt := ''Keine Vorkuehlung vorgeschrieben'';  End if;
 

We get the following:
ERROR:  Bad interval external representation 'vk days'

The variable 'heute' is declared as timestamp,
'vk' as integer!

What have we done wrong??

:(

Thanks in advance,

Willi, Albin

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Wilhelm Graiss
Altirdning 12
8952 Irdning
03682/22451/267