Subject Update only changed tuple/ execute if-statement via "execute statement"?
Author eric wulfhekel
Post date 2014-05-30T08:03:06Z
Hello,

I would be very happy if anybody could help me. I want to create a update trigger which sets the current date to a field "modified" if values has changed. I have a lot of tables with a lot of columns so i want to work with system table for that task. I build the if-statement within a select and wat to execute this statement

Like:

CREATE TRIGGER PLZTEST_MODIFIED FOR PLZTEST
ACTIVE BEFORE UPDATE POSITION 0
AS
declare variable stmt varchar(1024);
begin
for
    select 'if (new.' || rdb$field_name || ' is null and old.' ||
        rdb$field_name || ' is not null or new.' || rdb$field_name ||
        'is not null and old.' || rdb$field_name || ' is null or new.' ||
        rdb$field_name || ' <> old.' || rdb$field_name || ') then new.MODIFIED = current_timestamp;'
     from rdb$relation_fields
     where rdb$relation_name = 'PLZTEST'
     into :stmt
do
execute statement stmt;
end


The resulting statement looks good.
The problem here seems, that i could not execute statements starts with if. the error occur is

Dynamic SQL Error.
SQL error code = -104.
Token unknown - line 1, column 1.
if.

Or maybe is there another way to realise that?

Thank you in advance