Field level audit on SQL Server using Trigger - sql-server

Question

I am trying to write a trigger which would audit a table's every field - a row's old value and new value in a table. If any of the field has been modified, I need to save the fields old value and the new value along with field name in an audit table, as a new entry.
create trigger Trg_Institution_FieldAudit on Table1 AFTER UPDATE AS
DECLARE #OldName VARCHAR(30)
DECLARE #CurrentName VARCHAR(30)
DECLARE #OldId VARCHAR(30)
DECLARE #CurrentId VARCHAR(30)
DECLARE #modifiedBy VARCHAR(30)
If update(Name)
BEGIN
select #OldName = Name from deleted
select #CurrentName = Name from Inserted
select #OldId = ID from deleted
select #currentId = ID from Inserted
select #modifiedBy = modifiedBy from deleted
--INSERT statement for Name field alone
END;
This works fine for a small number of fields, but I have a lot of fields (more than 60), and I am not achieving the performance that is required, because of a lot of if conditions. Is there a better way of doing this? On top of this, there are concurrent updates that are happening to around 3 million records in this table, which makes a lot of things go wrong :(
EDIT: Only ONE row will get updated by an UPDATE statement

Answer 1

Oh my. Please avoid using a cursor whenever possible! You can easily use an insert statement with a select referencing the inserted and deleted tables. Below is a sample from one of my update triggers.
DECLARE #AuditTime DATETIME
SET #AuditTime = GetDate()
IF UPDATE([AccountManager])
INSERT INTO Audit.AuditHistory (AuditId, AuditDate, AuditTableName, EntityKey, AuditFieldName, OldValue, NewValue, FieldDisplayText, OldDisplayText, NewDisplayText, ModifiedBy)
SELECT NewId(),
#AuditTime,
'[tblOpportunity]',
cast(d.[GOTSID] AS varchar),
'[AccountManager]',
cast(d.[AccountManager] AS varchar(250)),
cast(i.[AccountManager] AS varchar(250)),
'Account Manager',
isnull(cast(d.[AccountManager] AS varchar(250)), ''),
isnull(cast(i.[AccountManager] AS varchar(250)), ''),
isnull(i.[ModifiedBy], '')
FROM deleted d
INNER JOIN inserted i ON d.GOTSID = i.GOTSID
WHERE d.[AccountManager] <> i.[AccountManager]
OR (d.[AccountManager] IS NOT NULL
AND i.AccountManager IS NULL)
OR (d.[AccountManager] IS NULL
AND i.AccountManager IS NOT NULL)

Answer 2

#marc_s is right, you have to re-construct your trigger and tables. here take example.
you need to put where condition in select #OldName = Name from deleted.
e.g.-
**
CREATE TRIGGER Trg_Institution_FieldAudit ON Table1 FOR UPDATE
AS
DECLARE #OldName VARCHAR(30)
DECLARE #CurrentName VARCHAR(30)
IF UPDATE (Name)
BEGIN
SET #OldName = Table1.Name FROM deleted
WHERE Table1.Name = deleted.Name;
SET #CurrentName = Table1.Name FROM inserted
WHERE Table1.Name = inserted.Name ;
--INSERT statement for old and new values.
END
GO**

Answer 3

After looking for an alternative for FOR EACH in SQL Server, I found that a CURSOR can be used. It serves the purpose, but need somebody to validate this.
CREATE TRIGGER Trg_Institution_FieldAudit_1 ON dbo.Institution FOR UPDATE as
-- DECLARE Variables
DECLARE institution_cursor CURSOR DYNAMIC FOR SELECT * FROM DELETED
OPEN institution_cursor FETCH NEXT FROM institution_cursor INTO -- #variables here
WHILE (##FETCH_STATUS = 0)
BEGIN
IF UPDATE(COL1)
BEGIN
INSERT INTO AuditTable VALUES (COL1, #prev, #next);
END;
FETCH NEXT FROM institution_cursor INTO -- #Variables here
END
CLOSE institution_cursor
DEALLOCATE institution_cursor