CREATE TRIGGER [dbo].[EmployeeInsert]
ON  [dbo].[APP_Employees]
AFTER INSERT
AS
BEGIN
SET NOCOUNT ON;

DECLARE @EmployeeID AS bigint

SELECT @EmployeeID = ID FROM inserted

UPDATE [dbo].[APP_Employees]
SET  [EmployeeTotalNumberOfAnnualLeave] = [EmployeeBalanceTheInitialNumberOfDaysOfAnnualLeaveIn]
WHERE ID=@EmployeeID

END
GO

SELECT @EmployeeID = ID FROM inserted

-- drop the existing trigger
DROP TRIGGER [dbo].[EmployeeInsert]
GO

-- create a new trigger
CREATE TRIGGER [dbo].[EmployeeInsert]
ON [dbo].[APP_Employees]
AFTER INSERT
AS
BEGIN
    SET NOCOUNT ON;

    -- update your table, using a set-based approach
    -- from the "Inserted" pseudo table which CAN and WILL
    -- contain multiple rows!
    UPDATE [dbo].[APP_Employees]
    SET  [EmployeeTotalNumberOfAnnualLeave] = i.[EmployeeBalanceTheInitialNumberOfDaysOfAnnualLeaveIn]
    FROM Inserted i
    WHERE ID = i.ID
END
GO

-- 1.1) Create the base of table 'MAN'
CREATE TABLE [dbo].[MAN](
    [DATETIME] [datetime] NOT NULL
) ON [PRIMARY]
GO

-- 1.2) Insert a record in it
INSERT INTO MAN VALUES ('04/06/1982')
GO

-- 1.3) Add some computed columns
ALTER TABLE MAN
ADD
    [DAY]       AS DATENAME(DAY, [DATETIME]),
    [MONTH]     AS MONTH([DATETIME]),
    [YEAR]      AS DATENAME(YEAR, [DATETIME]),
    [DAYNAME]   AS DATENAME(WEEKDAY, [DATETIME]),
    [AGE]       AS DATEDIFF(YEAR, [DATETIME], GETDATE())
GO

-- 1.4) See the result
SELECT * FROM MAN

SELECT * FROM MAN
-- 2.1) Create the table 'MAN' with all needed columns
CREATE TABLE [dbo].[MAN](
    [DATETIME]  [datetime]      NOT NULL,
    [DAY]       [int]           NULL,
    [MONTH]     [int]           NULL,
    [YEAR]      [int]           NULL,
    [DAYNAME]   [nvarchar](10)  NULL,
    [AGE]       [int]           NULL
) ON [PRIMARY]
GO

-- 2.2) Create Insert and update triggers in order to calculated values of the rest fields while inserting/updating
CREATE TRIGGER [dbo].[trCalculateRemainingDateFields] ON MAN
AFTER INSERT, UPDATE
AS
BEGIN
    SET NOCOUNT ON;

    UPDATE  MAN
    SET
        [DAY]       = DATENAME(DAY, MAN.[DATETIME]),
        [MONTH]     = MONTH(MAN.[DATETIME]),
        [YEAR]      = DATENAME(YEAR, MAN.[DATETIME]),
        [DAYNAME]   = DATENAME(WEEKDAY, MAN.[DATETIME]),
        [AGE]       = DATEDIFF(YEAR, MAN.[DATETIME], GETDATE())

    FROM    Inserted i
    WHERE   i.[DATETIME] = MAN.[DATETIME]
END
GO


-- 2.3) Insert a record in it
INSERT INTO MAN ([DATETIME]) VALUES ('04/06/1985')
GO

-- 2.4) See the result
SELECT * FROM MAN