After Trigger for Update and Insert failing - sql-server

Question

I am writing a trigger for keeping audit record for one table for Insert and Update records.
CREATE TABLE [dbo].[AppLog](
[TableName] [varchar](32) NOT NULL,
[ColumnName] [varchar](32) NOT NULL,
[RecordId] [varchar](20) NOT NULL,
[OldValue] [varchar](2000) NULL,
[NewValue] [varchar](2000) NULL,
[UpdatedBy] [varchar](200) NULL,
[UpdatedOn] [datetime] NULL
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[Persons](
[Personid] [int] IDENTITY(1,1) NOT NULL,
[LastName] [varchar](255) NOT NULL,
[FirstName] [varchar](255) NULL,
[Age] [int] NULL
) ON [PRIMARY]
GO
CREATE TRIGGER AuditRecord ON dbo.Persons
AFTER UPDATE, INSERT
AS
INSERT INTO AppLog
(TableName ,ColumnName ,RecordId ,OldValue ,NewValue ,UpdatedBy ,UpdatedOn )
SELECT 'Persons', 'LastName', COALESCE(i.Personid,NULL),
d.LastName, i.LastName, CURRENT_USER, GETDATE()
FROM Persons pv
LEFT JOIN INSERTED i ON pv.Personid = i.Personid
LEFT JOIN DELETED d ON pv.Personid = d.Personid;
GO
INSERT INTO Persons (FirstName,LastName,age)
VALUES ('Satish','Parida',40);
INSERT INTO Persons (FirstName,LastName,age)
VALUES ('SKP','Tada',90);
The last insert is failing as it is trying to insert null to recordid column in applog table, could someone explain or fix the issue.

Answer 1

The statement that is failing is the one below:
INSERT INTO Persons (FirstName,LastName,age)
VALUES ('SKP','Tada',90);
This is because in your Trigger you are using Persons are your "base" table and the performing a LEFT JOIN to both inserted and deleted. As result when you try to perform the above INSERT, values from the previous INSERT are used as well in the trigger's dataset. The person 'Parida' doesn't appear in the table inserted for your second INSERT, and so COALESCE(i.Personid,NULL) returns NULL; as I mentioned in my comment, there' no point using COALESCE to return NULL, as if an expression's value evaluates to NULL it will return NULL. As RecordID (which is what COALESCE(i.Personid,NULL) is being inserted into) can't have the value NULL the INSERT fails and the whole transaction is rolled back.
I suspect that what you want for your trigger is the below:
CREATE TRIGGER AuditRecord ON dbo.Persons
AFTER UPDATE, INSERT
AS BEGIN
INSERT INTO AppLog (TableName,
ColumnName,
RecordId,
OldValue,
NewValue,
UpdatedBy,
UpdatedOn)
SELECT 'Persons',
'LastName',
i.Personid,
d.LastName,
i.LastName,
CURRENT_USER,
GETDATE()
FROM inserted AS i
LEFT JOIN deleted AS d ON i.Personid = d.Personid;
END;
inserted will always have at least 1 row for an UPDATE or an INSERT. inserted would not for a DELETE, but your trigger won't fire on that DML event so using inserted as the "base" table seems the correct choice.

Answer 2

Following code should work
CREATE TABLE [dbo].[AppLog](
[TableName] [varchar](32) NOT NULL,
[ColumnName] [varchar](32) NOT NULL,
[RecordId] [varchar](20) NOT NULL,
[OldValue] [varchar](2000) NULL,
[NewValue] [varchar](2000) NULL,
[UpdatedBy] [varchar](200) NULL,
[UpdatedOn] [datetime] NULL
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[Persons](
[Personid] [int] IDENTITY(1,1) NOT NULL,
[LastName] [varchar](255) NOT NULL,
[FirstName] [varchar](255) NULL,
[Age] [int] NULL
) ON [PRIMARY]
GO
CREATE TRIGGER AuditRecord ON dbo.Persons
AFTER UPDATE, INSERT
AS
if exists(SELECT * from inserted) and exists (SELECT * from deleted)
BEGIN
INSERT INTO AppLog
(TableName ,ColumnName ,RecordId ,OldValue ,NewValue ,UpdatedBy ,UpdatedOn )
SELECT 'Persons', 'LastName', COALESCE(i.Personid,NULL),
d.LastName, i.LastName, CURRENT_USER, GETDATE()
FROM Persons pv
INNER JOIN INSERTED i ON pv.Personid = i.Personid
INNER JOIN DELETED d ON pv.Personid = d.Personid;
END
If exists (Select * from inserted) and not exists(Select * from deleted)
begin
INSERT INTO AppLog
(TableName ,ColumnName ,RecordId ,OldValue ,NewValue ,UpdatedBy ,UpdatedOn )
SELECT
'Persons', 'LastName',i.Personid,NULL,i.LastName,CURRENT_USER,GETDATE()
FROM
inserted AS i
END
GO
INSERT INTO Persons (FirstName,LastName,age)
VALUES ('Satish','Parida',40);
INSERT INTO Persons (FirstName,LastName,age)
VALUES ('SKP','Tada',90);
INSERT INTO Persons (FirstName,LastName,age)
VALUES ('abc','def',90);
INSERT INTO Persons (FirstName,LastName,age)
VALUES ('gg','hh',90);
UPDATE dbo.Persons SET LastName='Paridachanged' WHERE Personid=1
SELECT * FROM Persons
SELECT * FROM AppLog

Answer 3

USE KnockKnockDev;
GO
IF OBJECT_ID('dbo.AuditRecord', 'TR') IS NOT NULL
DROP TRIGGER dbo.AuditRecord;
GO
CREATE TRIGGER AuditRecord ON dbo.Persons
AFTER UPDATE, INSERT, DELETE
AS
DECLARE #Action as char(1)
DECLARE #Count as int
DECLARE #TableName as char(32)
DECLARE #ColumnName as char (32)
SET #TableName = 'Persons'
SET #ColumnName = 'LastName'
SET #Action = 'I' -- Set Action to 'I'nsert by default.
SELECT #Count = COUNT(*) FROM DELETED
IF #Count > 0
BEGIN
SELECT #Count = COUNT(*) FROM INSERTED
IF #Count > 0
SET #Action = 'U' -- Set Action to 'U'pdated.
ELSE
SET #Action = 'D' -- Set Action to 'D'eleted.
END
IF #Action = 'I'
BEGIN
INSERT INTO AppLog
(TableName ,ColumnName ,RecordId ,OldValue ,NewValue ,Action ,UpdatedBy ,UpdatedOn )
SELECT #TableName, #ColumnName, Personid,
NULL, LastName, #Action, CURRENT_USER, GETDATE()
FROM INSERTED;
END
ELSE IF #Action = 'D'
BEGIN
INSERT INTO AppLog
(TableName ,ColumnName ,RecordId ,OldValue ,NewValue ,Action ,UpdatedBy ,UpdatedOn )
SELECT #TableName, #ColumnName, Personid,
LastName, NULL, #Action, CURRENT_USER, GETDATE()
FROM DELETED;
END
ELSE
BEGIN
INSERT INTO AppLog
(TableName ,ColumnName ,RecordId ,OldValue ,NewValue ,Action ,UpdatedBy ,UpdatedOn )
SELECT #TableName, #ColumnName, i.Personid,
d.LastName, i.LastName, #Action, CURRENT_USER, GETDATE()
FROM Persons pv
INNER JOIN INSERTED i ON pv.Personid = i.Personid
INNER JOIN DELETED d ON pv.Personid = d.Personid;
END
GO