I just answered this question on StackOverflow about how to generically compare an inserted row to a deleted row within a trigger. I started by just commenting that it would be a good place to do a little code generation, but something about the problem wouldn’t let me put it down. Here’s what I came up with.
First I created a function that would return the query that would actually do the comparison. Notice that I’m comparing #inserted and #deleted rather than inserted and deleted. This is because we don’t have access to the inserted and deleted tables when we’re running the comparison query in an exec()
create function GetChangedRowsQuery( @TableName varchar(50), @PrimaryKeyColumnName varchar(50), @RowVersionColumnName varchar(50) = '' ) returns varchar(max) as begin declare @ColumnName varchar(50), @GetChangedRowsQuery varchar(max) select @GetChangedRowsQuery = 'select isnull(a.' + @PrimaryKeyColumnName + ', b.' + @PrimaryKeyColumnName + ') from #inserted a full join #deleted b on a.' + @PrimaryKeyColumnName + ' = b.' + @PrimaryKeyColumnName + ' where ' declare ColumnCursor cursor Read_Only for select Name from Sys.columns where object_id = Object_Id('Member') open ColumnCursor fetch next from ColumnCursor into @ColumnName while @@FETCH_STATUS = 0 begin if (@ColumnName != @PrimaryKeyColumnName and @ColumnName != @RowVersionColumnName) begin select @GetChangedRowsQuery = @GetChangedRowsQuery + '((a.' + @ColumnName + ' != b.' + @ColumnName + ' or a.' + @ColumnName + ' is null or b.' + @ColumnName + ' is null) and (a.' + @ColumnName + ' is not null or b.' + @ColumnName + ' is not null))' + char(13) + ' or ' end fetch next from ColumnCursor into @ColumnName end close ColumnCursor deallocate ColumnCursor select @GetChangedRowsQuery = substring(@GetChangedRowsQuery, 0, len(@GetChangedRowsQuery) -7) return @GetChangedRowsQuery end
Next, I created a trigger. It creates the #inserted and #deleted temp tables, get’s the query from the function, creates a temp table to hold the results. Then it inserts the result into the temp table. I’m just selecting the top 10 changed rows, but you could do whatever you needed to do with the changed rows at this point.
create trigger TestTrigger on Member for Insert, Update, Delete as begin select * into #Inserted from Inserted select * into #Deleted from Deleted declare @GetChangedRowsQuery varchar(max) select @GetChangedRowsQuery = dbo.GetChangedRowsQuery('MemberTrash', 'MemberId', '') create table #Temp (PrimaryKey int) insert into #Temp (PrimaryKey) exec (@GetChangedRowsQuery) select top 10 * from #Temp drop table #Temp drop table #Inserted drop table #Deleted end