I see my previous message is completely unreadable, so I am trying
again. In the meanwhile, I read in README.execute_statement.txt:

>>>

For all forms of EXECUTE STATEMENT SQL, the DSQL string can not
contain any parameters. All variable substitution into the static
part of the SQL statement should be performed before EXECUTE STATEMENT
<<<

So, this seems to be the problem (context variables are variables,
are not they?). Still looking for a workaround...

This was my previous message:

Hi all!!

I am trying to write a trigger to log changes performed in a table
into a txt file, which will be imported by another system (not to
firebird, but to a paradox table).

I want to store table name, operation, key field and all the fields
values. The 'easy' way is to write something like this:

SET TERM ^;
CREATE TRIGGER MY_TRIGGER
FOR MY_TABLE
AFTER INSERT OR UPDATE OR DELETE
AS
DECLARE VARIABLE TXT_LINE VARCHAR(1024);
BEGIN
IF ( INSERTING ) THEN
TXT_LINE
='MY_TABLE;I;'||NEW.FIELD1||';'||NEW.FIELD1||';'||NEW.FIELD2||';'|| ..
.. ;
ELSE
IF ( UPDATING ) THEN
TXT_LINE
= 'MY_TABLE;U;'||OLD.FIELD1||';'||NEW.FIELD1||';'||NEW.FIELD2||';'|| .
... ;
ELSE
TXT_LINE
= 'MY_TABLE;D;'||OLD.FIELD1||';'||OLD.FIELD1||';'||OLD.FIELD2||';'|| .
... ;
FILE_WRITE( 'MYFILE.TXT', TXT_LINE );
END;
SET TERM ;^

The problem is that if I add a new field to my table, I have to
change the trigger. So I would like to generate this
sentence 'dinamically'. Something like this:

SET TERM ^;
CREATE PROCEDURE AUX_WRITE( IN_LINE VARCHAR(1024) )
AS
BEGIN
FILE_WRITE( 'MYFILE.TXT', IN_LINE );
END^

CREATE TRIGGER MY_TRIGGER
FOR MY_TABLE
AFTER INSERT OR UPDATE OR DELETE
AS
DECLARE VARIABLE TXT_LINE VARCHAR(1024);
DECLARE VARIABLE TXT_COMMAND VARCHAR(1500);
DECLARE VARIABLE MY_CONTEXT CHAR(4);
DECLARE VARIABLE FIELD_NAME VARCHAR(30);
BEGIN
MY_CONTEXT = 'NEW';
IF ( INSERTING ) THEN
TXT_LINE = 'MY_TABLE;I;'||NEW.FIELD1;
ELSE
BEGIN
IF ( UPDATING ) THEN
TXT_LINE = 'MY_TABLE;U;'||OLD.FIELD1;
ELSE
BEGIN
TXT_LINE = 'MY_TABLE;D;'||OLD.FIELD1;
MY_CONTEXT = 'OLD';
END
END

FOR SELECT f.rdb$field_name FROM rdb$relation_fields f
WHERE f.rdb$relation_name='MY_TABLE'
ORDER BY f.rdb$field_position INTO :FIELD_NAME DO
TXT_LINE = :TXT_LINE || ';' || :MY_CONTEXT || '.' || :FIELD_NANE;

TXT_COMMAND = 'EXECUTE PROCEDURE AUX_WRITE( ' || TXT_LINE || ' );'
EXECUTE STATEMENT( TXT_COMMAND );
END^
SET TERM ;^

The generated sentence is right, that is, executing it directly works
fine, but having it as string and executing through EXECUTE STATEMENT
I get an error telling >> 'NEW.FIELD1' IS AN UNKNOWN COLUMN

Probably there is something I am misunderstanding... any workaround??

Thanks in advance for your help, and sorry for the lenght of my first
message...

Puri Vidal