/*
This trigger audit trails all changes made to a table.
It will place in the table Audit all inserted, deleted, changed columns in the table on which it is placed.
It will put out an error message if there is no primary key on the table
You will need to change @TableName to match the table to be audit trailed
*/

--Set up the tables
if exists (select * from sysobjects where id = object_id(N'[dbo].[Audit]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[Audit]
go
create table Audit (Type char(1), TableName varchar(128), PK varchar(1000), FieldName varchar(128), OldValue varchar(1000), NewValue varchar(1000), UpdateDate datetime, UserName varchar(128))
go
if exists (select * from sysobjects where id = object_id(N'[dbo].[trigtest]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[trigtest]
go
create table trigtest (i int not null, j int not null, s varchar(10), t varchar(10))
go
alter table trigtest add constraint pk primary key (i, j)
go

create trigger tr_trigtest on trigtest for insert, update, delete
as

declare @bit int ,
	@field int ,
	@maxfield int ,
	@char int ,
	@fieldname varchar(128) ,
	@TableName varchar(128) ,
	@PKCols varchar(1000) ,
	@sql varchar(2000), 
	@UpdateDate varchar(21) ,
	@UserName varchar(128) ,
	@Type char(1) ,
	@PKSelect varchar(1000)
	
	select @TableName = 'trigtest'

	-- date and user
	select 	@UserName = system_user ,
		@UpdateDate = convert(varchar(8), getdate(), 112) + ' ' + convert(varchar(12), getdate(), 114)

	-- Action
	if exists (select * from inserted)
		if exists (select * from deleted)
			select @Type = 'U'
		else
			select @Type = 'I'
	else
		select @Type = 'D'
	
	-- get list of columns
	select * into #ins from inserted
	select * into #del from deleted
	
	-- Get primary key columns for full outer join
	select	@PKCols = coalesce(@PKCols + ' and', ' on') + ' i.' + c.COLUMN_NAME + ' = d.' + c.COLUMN_NAME
	from	INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk ,
		INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
	where 	pk.TABLE_NAME = @TableName
	and	CONSTRAINT_TYPE = 'PRIMARY KEY'
	and	c.TABLE_NAME = pk.TABLE_NAME
	and	c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME
	
	-- Get primary key select for insert
	select @PKSelect = coalesce(@PKSelect+'+','') + '''<' + COLUMN_NAME + '=''+convert(varchar(100),coalesce(i.' + COLUMN_NAME +',d.' + COLUMN_NAME + '))+''>''' 
	from	INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk ,
		INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
	where 	pk.TABLE_NAME = @TableName
	and	CONSTRAINT_TYPE = 'PRIMARY KEY'
	and	c.TABLE_NAME = pk.TABLE_NAME
	and	c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME
	
	if @PKCols is null
	begin
		raiserror('no PK on table %s', 16, -1, @TableName)
		return
	end
	
	select @field = 0, @maxfield = max(ORDINAL_POSITION) from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME = @TableName
	while @field < @maxfield
	begin
		select @field = min(ORDINAL_POSITION) from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME = @TableName and ORDINAL_POSITION > @field
		select @bit = (@field - 1 )% 8 + 1
		select @bit = power(2,@bit - 1)
		select @char = ((@field - 1) / 8) + 1
		if substring(COLUMNS_UPDATED(),@char, 1) & @bit > 0 or @Type in ('I','D')
		begin
			select @fieldname = COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME = @TableName and ORDINAL_POSITION = @field
			select @sql = 		'insert Audit (Type, TableName, PK, FieldName, OldValue, NewValue, UpdateDate, UserName)'
			select @sql = @sql + 	' select ''' + @Type + ''''
			select @sql = @sql + 	',''' + @TableName + ''''
			select @sql = @sql + 	',' + @PKSelect
			select @sql = @sql + 	',''' + @fieldname + ''''
			select @sql = @sql + 	',convert(varchar(1000),d.' + @fieldname + ')'
			select @sql = @sql + 	',convert(varchar(1000),i.' + @fieldname + ')'
			select @sql = @sql + 	',''' + @UpdateDate + ''''
			select @sql = @sql + 	',''' + @UserName + ''''
			select @sql = @sql + 	' from #ins i full outer join #del d'
			select @sql = @sql + 	@PKCols
			select @sql = @sql + 	' where i.' + @fieldname + ' <> d.' + @fieldname 
			select @sql = @sql + 	' or (i.' + @fieldname + ' is null and  d.' + @fieldname + ' is not null)' 
			select @sql = @sql + 	' or (i.' + @fieldname + ' is not null and  d.' + @fieldname + ' is null)' 
			exec (@sql)
		end
	end
go


insert trigtest select 1,1,'hi', 'bye'
insert trigtest select 2,2,'hi', 'bye'
insert trigtest select 3,3,'hi', 'bye'
select * from Audit
select * from trigtest
update trigtest set s = 'hibye' where i <> 1
update trigtest set s = 'bye' where i = 1
update trigtest set s = 'bye' where i = 1
update trigtest set t = 'hi' where i = 1
select * from Audit
select * from trigtest
delete trigtest
select * from Audit
select * from trigtest

go
drop table Audit
go
drop table trigtest
go