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 g

Answer 1

This is adapted from Juan Carlos Velez's answer. I modified it to account for compound primary keys, and for column names that include spaces. Also, I commented it throughout so that someone who wants to modify it for their purposes can understand what is happening at each step, if the code is not clear to them.

-- This stops the message that shows the count of the number of rows affected from being returned as part of the result set.
set nocount on

-- If the Audit table doesn't exist, create it.
if not exists(select * from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'Audit')
create table Audit
(
    AuditID [int] identity(1,1) not null,
    [Type] char(1), 
    TableName nvarchar(128), 
    PKFields nvarchar(max),
    PKValues nvarchar(max),
    FieldName nvarchar(128), 
    OldValue nvarchar(max), 
    NewValue nvarchar(max), 
    UpdateDate datetime, 
    UserName nvarchar(128)
)
go

-- Variables for the dynamic SQL and table name.
declare @tr nvarchar(max),
@tableName sysname

-- Get the first table in database. Skip over views and a few specified tables.
select @tableName = min(TABLE_NAME) from INFORMATION_SCHEMA.TABLES where TABLE_TYPE = 'BASE TABLE' and TABLE_NAME <> 'sysdiagrams' and TABLE_NAME <> 'Audit'
---- If you want to specify certain tables, uncomment the next line and add your table names.
--and (TABLE_NAME = 'IGAs' or TABLE_NAME = 'IGABudgets' or TABLE_NAME = 'Resolutions' or TABLE_NAME = 'RTAProjects' or TABLE_NAME = 'RTASubProjects')

-- Loop through the tables in the database and create an audit trigger on each one.
while @tableName is not null
begin

    -- If a trigger of the same name already exists, delete it.
    exec('if OBJECT_ID (''' + @tableName + '_ChangeTracking'', ''TR'') is not null drop trigger ' + @tableName + '_ChangeTracking')

    -- Check if there is a primary key. If not, throw an error.
    if (select count(*) from INFORMATION_SCHEMA.TABLE_CONSTRAINTS c, INFORMATION_SCHEMA.KEY_COLUMN_USAGE u where c.TABLE_NAME = @tableName and c.CONSTRAINT_TYPE = 'PRIMARY KEY' and u.TABLE_NAME = c.TABLE_NAME and u.CONSTRAINT_NAME = c.CONSTRAINT_NAME) = 0
    begin
        raiserror('Error: There is no primary key on table %s', 16, -1, @tableName)
        return
    end

    -- Create the trigger.
    select @tr = 'create trigger ' + @tableName + '_ChangeTracking on ' + @tableName + ' for insert, update, delete as

    -- Misc variables.
    declare @table nvarchar(128),
    @fieldName nvarchar(128) = '''',
    @type char(1),
    @pkJoin nvarchar(max),
    @pkSelect nvarchar(max),
    @pkFields nvarchar(max),
    @pkValues nvarchar(max),
    @updateDate nvarchar(30) = convert(varchar(30), getdate(), 22),
    @user nvarchar(128) = system_user,
    @sql nvarchar(max),
    @params nvarchar(max) = N''@out nvarchar(max) output'',
    @fieldIndex int = 0,
    @maxField int,
    @bit int,
    @char int

    -- Get the table name.
    select @table = object_name(parent_id) from sys.triggers where object_id = @@PROCID

    -- Get the modification type: U = update, I = insert, D = delete
    if exists (select * from inserted)
        if exists (select * from deleted)
            select @type = ''U''
        else select @type = ''I''
    else select @type = ''D''

    -- Save the inserted and deleted values into temp tables.
    select * into #ins from inserted
    select * into #del from deleted

    -- Get the number of columns in the table.
    select @maxField = max(columnproperty(object_id(@table), COLUMN_NAME, ''ColumnID'')) from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME = @table

    -- Get the primary key join relationship(s).
    select @pkJoin = coalesce(@pkJoin + '' and'', '' on'') + '' i.['' + u.COLUMN_NAME + ''] = d.['' + u.COLUMN_NAME + '']''
    from INFORMATION_SCHEMA.TABLE_CONSTRAINTS c, INFORMATION_SCHEMA.KEY_COLUMN_USAGE u
    where c.TABLE_NAME = @table
    and c.CONSTRAINT_TYPE = ''PRIMARY KEY''
    and u.TABLE_NAME = c.TABLE_NAME
    and u.CONSTRAINT_NAME = c.CONSTRAINT_NAME

    -- Get the primary key field name(s).
    select @pkFields = coalesce(@pkFields + '', '', '''') + ''['' + u.COLUMN_NAME + '']''
    from INFORMATION_SCHEMA.TABLE_CONSTRAINTS c, INFORMATION_SCHEMA.KEY_COLUMN_USAGE u
    where c.TABLE_NAME = @table
    and c.CONSTRAINT_TYPE = ''PRIMARY KEY''
    and u.TABLE_NAME = c.TABLE_NAME
    and u.CONSTRAINT_NAME = c.CONSTRAINT_NAME

    -- Get the primary key field(s) for select statement.
    select @pkSelect = coalesce(@pkSelect + '' + '''', '''' + '', '''') + ''convert(nvarchar(max), ['' + u.COLUMN_NAME + ''])''
    from INFORMATION_SCHEMA.TABLE_CONSTRAINTS c, INFORMATION_SCHEMA.KEY_COLUMN_USAGE u
    where c.TABLE_NAME = @table
    and c.CONSTRAINT_TYPE = ''PRIMARY KEY''
    and u.TABLE_NAME = c.TABLE_NAME
    and u.CONSTRAINT_NAME = c.CONSTRAINT_NAME

    -- Get the primary key field value(s).
    if (@type = ''D'')
    begin
        set @sql = ''select @out = '' + @pkSelect + '' from #del''
        exec sp_executesql @sql, @params, @out = @pkValues output
    end
    else
    begin 
        set @sql = ''select @out = '' + @pkSelect + '' from #ins''
        exec sp_executesql @sql, @params, @out = @pkValues output
    end

    -- Loop through each field in the inserted table.
    while @fieldIndex < @maxField
    begin

        -- Iterate the fieldIndex.
        select @fieldIndex = min(ORDINAL_POSITION) from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME = @table and columnproperty(object_id(@table), COLUMN_NAME, ''ColumnID'') > @fieldIndex 

        -- If the column in scope has been modified, insert a record into the Audit table.
        select @bit = (@fieldIndex - 1)% 8 + 1
        select @bit = POWER(2, @bit - 1)
        select @char = ((@fieldIndex - 1) / 8) + 1
        if substring(columns_updated(), @char, 1) & @bit > 0 or @Type IN (''I'', ''D'')
        begin

            -- Get the name of the field whose ColumnID equals the current fieldIndex.
            select @fieldName = ''['' + COLUMN_NAME + '']'' from INFORMATION_SCHEMA.COLUMNS 
            where TABLE_NAME = @table and columnproperty(object_id(@table), COLUMN_NAME, ''ColumnID'') = @fieldIndex '

    -- Select statements have a length limitation. End the statement, then add the rest.
    select @tr = @tr + '

            set @sql = ''insert into Audit (Type, TableName, PKFields, PKValues, FieldName, OldValue, NewValue, UpdateDate, UserName) select '''''' + @type + '''''', '''''' + @table + '''''', '''''' + @pkFields + '''''', '''''' + @pkValues + '''''', '''''' + @fieldName + '''''', convert(nvarchar(max), d.'' + @fieldName + ''), convert(nvarchar(max), i.'' + @fieldName + ''), '''''' + @updateDate + '''''', '''''' + @user + '''''' from #ins i full outer join #del d'' + @pkJoin + '' where i.'' + @fieldName + '' <> d.'' + @fieldName + '' or (i.'' + @fieldName + '' is null and d.'' + @fieldName + '' is not null) or (i.'' + @fieldName + '' is not null and d.'' + @fieldName + '' is null)''

            --print(@sql)
            exec(@sql)

        end
    end'

    ---- This is if you want to see the statement that is generated rather than execute it.
    --select @tr

    -- Execute the trigger statement.
    exec(@tr)

    -- Iterate the table name.
    select @tableName = min(TABLE_NAME) from INFORMATION_SCHEMA.TABLES 
    where TABLE_NAME > @tableName and
    TABLE_TYPE = 'BASE TABLE' and TABLE_NAME <> 'sysdiagrams' and TABLE_NAME <> 'Audit'
    ---- If you want to specify certain tables, uncomment the next line and add your table names.
    --and (TABLE_NAME = 'IGAs' or TABLE_NAME = 'IGABudgets' or TABLE_NAME = 'Resolutions' or TABLE_NAME = 'RTAProjects' or TABLE_NAME = 'RTASubProjects')

end