How to Debug Trigger

set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [dbo].[leave] ON [dbo].[attLeaveApplication]
AFTER UPDATE

AS 
declare @leaveAppId as numeric
declare @leaveId as numeric
declare @empid as varchar
declare @duration as numeric
declare @leavetype as varchar
declare @OP as numeric

select @leaveAppId=[LeaveAppId],@empid=[EmpID],@duration=[ApprDuration],@leaveId=[LeaveId] from inserted where [ApprFlag]=1

select @leavetype=[LeaveType] from attLeaveTypeMaster where [LeaveId]=@leaveId


if @leavetype='CL'
Begin
select @OP=[CLCL] from attLeaveTransaction where [EmpId]=@empid and DATEPART(Month,[Month])=DATEPART(Month,GetDate())
set @OP = @OP - @duration
update attLeaveTransaction set [CLCL]=@OP where [EmpId]=@empid and DATEPART(Month,[Month])=DATEPART(Month,GetDate())
END
if @leavetype='PL'
Begin
select @OP=[PLCL] from attLeaveTransaction where [EmpId]=@empid and DATEPART(Month,[Month])=DATEPART(Month,GetDate())
set @OP = @OP - @duration
update attLeaveTransaction set [PLCL]=@OP where [EmpId]=@empid and DATEPART(Month,[Month])=DATEPART(Month,GetDate())
END
if @leavetype='SL'
Begin
select @OP=[SLCL] from attLeaveTransaction where [EmpId]=@empid and DATEPART(Month,[Month])=DATEPART(Month,GetDate())
set @OP = @OP - @duration
update attLeaveTransaction set [SLCL]=@OP where [EmpId]=@empid and DATEPART(Month,[Month])=DATEPART(Month,GetDate())
END