Log record changes in SQL server in an audit table

Take a look at this article on Simple-talk.com by Pop Rivett. It walks you through creating a generic trigger that will log the OLDVALUE and the NEWVALUE for all updated columns. The code is very generic and you can apply it to any table you want to audit, also for any CRUD operation i.e. INSERT, UPDATE and DELETE. The only requirement is that your table to be audited should have a PRIMARY KEY (which most well designed tables should have anyway).

Here’s the code relevant for your GUESTS Table.

1. Create AUDIT Table.

    IF NOT EXISTS
          (SELECT * FROM sysobjects WHERE id = OBJECT_ID(N'[dbo].[Audit]') 
                   AND OBJECTPROPERTY(id, N'IsUserTable') = 1)
           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

2. CREATE an UPDATE Trigger on the GUESTS Table as follows.

    CREATE TRIGGER TR_GUESTS_AUDIT ON GUESTS FOR UPDATE
    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)
           
    
    --You will need to change @TableName to match the table to be audited. 
    -- Here we made GUESTS for your example.
    SELECT @TableName="GUESTS"
    
    -- date and user
    SELECT         @UserName = SYSTEM_USER ,
           @UpdateDate = CONVERT (NVARCHAR(30),GETDATE(),126)
    
    -- 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 "'' + @Type + ''',''' 
           + @TableName + ''',' + @PKSelect
           + ',''' + @fieldname + ''''
           + ',convert(varchar(1000),d.' + @fieldname + ')'
           + ',convert(varchar(1000),i.' + @fieldname + ')'
           + ',''' + @UpdateDate + ''''
           + ',''' + @UserName + ''''
           + ' from #ins i full outer join #del d'
           + @PKCols
           + ' 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)' 
                   EXEC (@sql)
           END
    END
    
    GO