SQL Server 2017

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CREATE TABLE [dbo].[EmployeeMonthlyBudget](
[Name] [nvarchar](50) NULL,
[Budget_Day] [money] NULL,
[DateCreated] [datetime] NULL,
[DateDeleted] [datetime] NULL
) 
INSERT [dbo].[EmployeeMonthlyBudget] ([Name], [Budget_Day], [DateCreated], 
[DateDeleted]) VALUES (N'SAM', 20.0000, CAST(N'2018-01-01T00:00:00.000' AS 
DateTime), CAST(N'2018-10-01T00:00:00.000' AS DateTime))

INSERT [dbo].[EmployeeMonthlyBudget] ([Name], [Budget_Day], [DateCreated], 
[DateDeleted]) VALUES (N'ROB', 10.0000, CAST(N'2018-01-01T00:00:00.000' AS 
DateTime), NULL)

INSERT [dbo].[EmployeeMonthlyBudget] ([Name], [Budget_Day], [DateCreated], 
[DateDeleted]) VALUES (N'TAM', 5.0000, CAST(N'2018-01-01T00:00:00.000' AS 
DateTime), CAST(N'2018-05-01T00:00:00.000' AS DateTime))

INSERT [dbo].[EmployeeMonthlyBudget] ([Name], [Budget_Day], [DateCreated], 
[DateDeleted]) VALUES (N'TAN', 100.0000, CAST(N'2018-01-01T00:00:00.000' AS 
DateTime), NULL)   
4 rows affected

SELECT 
  *, [Budget_Day]*DATEDIFF(day,[DateCreated],isnull([DateDeleted],GETDATE())) as TotalSpent
from 
   [dbo].[EmployeeMonthlyBudget]


Name
Budget_Day
DateCreated
DateDeleted
TotalSpent


SAM
20.0000
01/01/2018 00:00:00
01/10/2018 00:00:00
5460.0000

ROB
10.0000
01/01/2018 00:00:00
null
2980.0000

TAM
5.0000
01/01/2018 00:00:00
01/05/2018 00:00:00
600.0000

TAN
100.0000
01/01/2018 00:00:00
null
29800.0000

Name	Budget_Day	DateCreated	DateDeleted	TotalSpent
SAM	20.0000	01/01/2018 00:00:00	01/10/2018 00:00:00	5460.0000
ROB	10.0000	01/01/2018 00:00:00	null	2980.0000
TAM	5.0000	01/01/2018 00:00:00	01/05/2018 00:00:00	600.0000
TAN	100.0000	01/01/2018 00:00:00	null	29800.0000