Ignore Two Columns in Update Trigger

Question

I am using the code below in a trigger. I have two columns that are updated by a windows service every 60 minutes in the table I am monitoring. How can I ignore the two columns from writing to the audit table.

ALTER trigger [dbo].[tMonitors_ChangeTracking] on [dbo].[tMonitors] 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),
@PKFieldSelect varchar(1000),
@PKValueSelect varchar(1000)

select @TableName = 'tMonitors'

-- 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 fields select for insert
select @PKFieldSelect = coalesce(@PKFieldSelect+'+','') + '''' + 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

select @PKValueSelect = coalesce(@PKValueSelect+'+','') + '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 tMonitors_Audit (Type, TableName, PrimaryKeyField, PrimaryKeyValue, FieldName, OldValue, NewValue, UpdateDate, UserName)'
select @sql = @sql + ' select ''' + @Type + ''''
select @sql = @sql + ',''' + @TableName + ''''
select @sql = @sql + ',' + @PKFieldSelect
select @sql = @sql + ',' + @PKValueSelect
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

Answer 1

You can access the complete list of columns changed using COLUMNS_UPDATED() and compare it to pre-defined bit patterns. For tables with many columns, calculating the bit positions can be easier than listing out UPDATED(every) OR UPDATED(other) OR UPDATED(column).

For example, for a table:

CREATE TABLE Users
(
    UserID INT NOT NULL PRIMARY KEY IDENTITY,
    Name nvarchar(255) NOT NULL,
    EmailAddress nvarchar(255) NOT NULL,
    LastPageViewDate datetime NULL,
    GroupID INT NOT NULL
);

where you want to ignore updates to LastPageViewDate. You can determine the bitmask via:

SELECT name, column_id FROM sys.columns WHERE object_id = OBJECT_ID('dbo.Users')

name                 column_id
-------------------- -----------
UserID               1
Name                 2
EmailAddress         3
LastPageViewDate     4
GroupID              5

The trigger can then check for the little-endian bitmask 0x08 ignoring trailing 0's:

CREATE TRIGGER dbo.TR_IUD_Users_LogEdit
    ON dbo.Users 
    AFTER INSERT, UPDATE
AS
BEGIN
    SET NOCOUNT ON;

    -- Ignore page view logging caused by
    -- UPDATE Users SET LastPageViewDate = GETDATE() WHERE UserID = @UserID
    -- Bit 4 == LastPageViewDate
    IF COLUMNS_UPDATED() = 0x08 RETURN;

    -- For forward compatibility, you can ignore unchanged new columns added
    -- by RTRIM'ing the '0's (required since 0x08 != 0x0800)
    --
    --IF REPLACE(RTRIM(REPLACE(CONVERT(varchar(max), COLUMNS_UPDATED(), 2), '0', ' ')), ' ', '0') IN ('08')
    --  RETURN;

    /* Snipped trigger body */
END
GO

Answer 2

The simple approach, assuming these columns to ignore are only updated during this hourly process:

IF NOT (UPDATE(col_to_ignore_1) AND UPDATE(col_to_ignore_2))
BEGIN
    ... 
    EXEC(@sql);
END

Otherwise you can build a similar list based on INFORMATION_SCHEMA.COLUMNS, so that the logging only happens when at least one of the other columns is updated, that would end up like this:

IF (UPDATE(col_to_audit_1) OR UPDATE(col_to_audit_2) ... )
BEGIN
    ... 
    EXEC(@sql);
END

It is not clear from your question whether you want to ignore these two columns always, or only when this hourly process runs. Perhaps another idea is to use a transaction and disable the trigger for this update... it will obviously make the trigger much less complicated.

Answer 3

You can specify which columns you want to pay attention to by using the "UPDATE(column_name)" syntax, like so:

CREATE TRIGGER trigger_name ON tablename
FOR insert, update, delete
AS
SET NOCOUNT ON
IF ( UPDATE(Column1) OR UPDATE(Column2))
BEGIN
  --your sql here
END

Other options are available at the official documentation.