> query:
> update mytable set field_a=XXX where yyyyy;
>
> mytrigger: before update
> if(new.field_b>0) then
>      dosomething;
> else
>      dosomethingelse;
>
> the trigger must operate only when i update field_b not when i'm updating 
> field_A.
>
> Calling the first query new.field_b is always '0' and 'dosomethingelse' is 
> executed; checking for "field_b is not null" is 
> useless, it's '0'.
> There is a way to recognize that the query is not altering field_b?

if (new.field_b = old.field_b) then ...

or, if there can be nulls

if (new.field_b is not distinct from old.field_b) then ...

Ivan 

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