Sql trigger to save changes to an audit trail table

Question

I started on an ADS sql table trigger to store changes done on one particular table. Here is the idea:

//-------- sql trigger to store changes on patients table to auditLog Table
//----------------------------------------------------------------------
declare cChanges Char( 5000 );
declare allColumns Cursor ;
declare FieldName Char( 25 );
declare StrSql  Char( 255 );
declare @new cursor as select * from __new;
declare @old cursor as select * from __old; 
open @old; 
fetch @old;
open @new; 
fetch @new;
Set cChanges = '';
Open AllColumns as Select * from system.columns where parent = 'patients';
while fetch allColumns DO
// Try
   FieldName = allColumns.Name;
   StrSql = 'IF @new.'+FieldName
          + '<> @old.'+FieldName
          +' and @old.'+FieldName + '<> [ ] THEN ' 
                       + 'cChanges = Trim( '+cChanges+' ) + @old.'+FieldName
                                   + ' Changed to ' + '@new.'+fieldname
                                   + ' | '+ 'ENDIF ; ' ;
   Execute Immediate StrSql ;
//    Catch ALL
//    End Try;
End While;
if cChanges <> '' THEN
    Insert Into AuditLog ( TableKey, Patient, [table], [user], creation, Changes ) 
         values( @new.patient, @new.patient, [Patietns], User(), Now(), cChanges ) ;
ENDIF;
CLOSE AllColumns;
//--------------------------

The above trigger code errors with reporting variable cChanges does not exists.

Can someone help?

Reinaldo.

May not be pertinent but is "values( @new.patient, @new.patient, [Patietns], User()..." a typo (ie [Patietns]? — Chris Walton, Apr 01 '11 at 23:19

Pepto · Answer 1 · 2011-04-02T00:09:22.567

I believe the problem has to do with your dynamic SQl attempting to set a value declared in your trigger body.

e.g. Your cChanges = TRIM( statement might be causing the problem since cChanges does not exist that context.

You should use binding variables to accomplish this instead of attempting to set using the = sign.

You can see in their docs they say you cannot access those variables directly by going to

http://devzone.advantagedatabase.com/dz/webhelp/advantage9.1/advantage_sql/sql_psm_script/execute_immediate.htm

score 1 · Accepted Answer · answered Apr 08 '11 at 21:38

The problem is indeed that you cannot access local variables in the scripted executed immediately. What you can do to get around the problem is to use temporary table:

//-------- sql trigger to store changes on patients table to auditLog Table
//----------------------------------------------------------------------
declare cChanges Char( 5000 );
declare allColumns Cursor ;
declare FieldName Char( 25 );
declare StrSql  Char( 255 );
Set cChanges = '';
Open AllColumns as Select * from system.columns where parent = 'patients';
while fetch allColumns DO
// Try
   FieldName = allColumns.Name;

   StrSql = 'SELECT n.FieldName newVal,'
            + 'o.FieldName oldVal '
            + 'INTO #MyTrigTable '
            + 'FROM __new n, __old o';

   EXECUTE IMMEDIATE strSQL;

   IF ( SELECT oldVal FROM #myTrigTable ) <> '' THEN
      IF ( SELECT newVal FROM #myTrigTable ) <> ( SELECT oldVal FROM #myTrigTable ) THEN
         cChanges = 'Construct_SomeThing_Using_#myTrigTable_or_a_cursorBasedOn#MyTrigTable';
         INSERT INTO AuditLog ( TableKey, Patient, [table], [user], creation, Changes ) 
         SELECT patient, patient, 'Patietns', User(), Now(), cChages FROM __new ;
      END;
   END;
   DROP TABLE #myTrigTable;
//    Catch ALL
//    End Try;
End While;
CLOSE AllColumns;
//--------------------------

Sql trigger to save changes to an audit trail table

2 Answers2