Ignore Two Columns in Update Trigger - sql

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

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 2

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.

Answer 3

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