I want to track all changes to a table (documents) by inserting just one row into another table (documents_log) each time a row is updated in the documents table.

The problem I am having with the trigger below is that it seems to fire for every column that is changed, instead of just one time for the row update.

For example, if three columns are changed when a row in the documents table is updated, then three rows are inserted in the documents_log table.
If two columns are changed when a row in the documents table is updated, then two rows are inserted in the documents_log table.
If only one column is changed when a row in the documents table is updated, then one row is inserted in the documents_log table.

What do I need to do to the trigger so that only one row is inserted into the documents_log table when two or more columns are changed when a single row is updated in the documents table?

Documents Table:  dm_column_1, dm_column_2, dm_column_3
Documents_Log Table:  dl_column_1, dl_column_2, dl_column_3

SET TERM ^ ;
CREATE TRIGGER documents_after_u FOR documents ACTIVE
AFTER UPDATE POSITION 3
AS
 BEGIN
   INSERT INTO documents_log
     (dl_column_1, dl_column_2, dl_column_3)
   VALUES
     (new.dm_column_1, new.dm_column_2, new.dm_column_3);
 END^
SET TERM ; ^

Thank you,

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