Log changes to database table with trigger

Question

I am looking for a good way to log changes that occur on a particular set of tables in my SQL Server 2005 database. I believe the best way to do this is through a trigger that get's executed on updates and deletes. Is there anyway to grab the actual statement that is being ran? Once I have the statement I can easily log it someplace else (other DB table). However, I have not found an easy way (if possible) to grab the SQL statement that is being ran.

Answer 1

If you just want to keep a log of all transactions (insert, update and delete) in some database tables, then you can run the following script:

IF NOT EXISTS(SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME= 'Audit')
  CREATE TABLE LogTable
  (
    LogID [int]IDENTITY(1,1) NOT NULL,
    Type char(1), 
    TableName varchar(128), 
    PrimaryKeyField varchar(1000), 
    PrimaryKeyValue varchar(1000), 
    FieldName varchar(128), 
    OldValue varchar(1000), 
    NewValue varchar(1000), 
    UpdateDate datetime DEFAULT (GetDate()), 
    UserName varchar(128)
  )
GO

DECLARE @sql varchar(8000), @TABLE_NAME sysname
SET NOCOUNT ON

SELECT @TABLE_NAME= MIN(TABLE_NAME)
FROM INFORMATION_SCHEMA.Tables 
WHERE 
--query for table that you want to audit
TABLE_TYPE= 'BASE TABLE' 
AND TABLE_NAME!= 'sysdiagrams'
AND TABLE_NAME!= 'LogTable'
AND TABLE_NAME!= 'one table to not record de log';

WHILE @TABLE_NAME IS NOT NULL
  BEGIN

  SELECT 'PROCESANDO ' + @TABLE_NAME;

  EXEC('IF OBJECT_ID (''' + @TABLE_NAME+ '_ChangeTracking'', ''TR'') IS NOT NULL DROP TRIGGER ' + @TABLE_NAME+ '_ChangeTracking')


  SELECT @sql = 'create trigger ' + @TABLE_NAME+ '_ChangeTracking on ' + @TABLE_NAME+ ' 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 = ''' + @TABLE_NAME+ '''

        -- 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(comma deparated)           
        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

        -- Get primary key values for insert(comma deparated as varchar)           
        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 @sql = ''insert LogTable(Type, TableName, PrimaryKeyField, PrimaryKeyValue, UserName)''
        select @sql = @sql + '' select '''''' + @Type + ''''''''
        select @sql = @sql + '','''''' + @TableName + ''''''''
        select @sql = @sql + '','' + @PKFieldSelect
        select @sql = @sql + '','' + @PKValueSelect
        select @sql = @sql + '','''''' + @UserName + ''''''''

        select @sql = @sql + '' from #ins i full outer join #del d''
        select @sql = @sql + @PKCols        

        exec (@sql)
    ';
  SELECT @sql
  EXEC(@sql)


  SELECT @TABLE_NAME= MIN(TABLE_NAME) FROM INFORMATION_SCHEMA.Tables 
    WHERE TABLE_NAME> @TABLE_NAME
    --query for table that you want to audit
    AND TABLE_TYPE= 'BASE TABLE' 
    AND TABLE_NAME!= 'sysdiagrams'
    AND TABLE_NAME!= 'LogTable'
    AND TABLE_NAME!= 'one table to not record de log';
END

Answer 2

You should be able to accomplish this using the system management views.

An example would be something like this:

SELECT er.session_id,
  er.status,
  er.command,
  DB_NAME(database_id) AS 'DatabaseName',
  user_id,
  st.text
FROM sys.dm_exec_requests AS er
  CROSS APPLY sys.dm_exec_sql_text(er.sql_handle) AS st
WHERE er.session_id = @@SPID;

I'm not sure this will be as useful to you as a more data-centric logging mechanism might be, though.

Answer 3

Don't forget that your logging will be part of the transaction so if there is an error and you rollback the transaction, your log will also be deleted.

Answer 4

MSSQL has virtual tables named 'Inserted' and 'Deleted', which contain newly-inserted and/or newly-deleted and/or newly-updated data records, which you can access from a trigger ... I use these, to know what data has changed (that's instead of being told what statement changed the data).