Update from in SQL Server (lookup)

USE Arm_DB
Go

CREATE TABLE TBL_ARM1
(
ID INT IDENTITY(1,1)
,Title Nvarchar(50)
)

Go

CREATE TABLE TBL_Arm2
(
ID INT Identity(1,1)
,Name Nvarchar(50)
,Arm1_ID Int
,Arm_Title Nvarchar(50)
)


GO 
INSERT INTO TBL_ARM1 VALUES ('Arm1_1')
INSERT INTO TBL_ARM1 VALUES ('Arm1_2')
INSERT INTO TBL_ARM1 VALUES ('Arm1_3')

Go

INSERT INTO TBL_Arm2 (Name ,Arm_Title) VALUES('Mehran','Arm1_1')
INSERT INTO TBL_Arm2 (Name ,Arm_Title) VALUES('Mehran2','Arm1_2')
INSERT INTO TBL_Arm2 (Name ,Arm_Title) VALUES('Mehran3','Arm1_3')



SELECT * FROM TBL_Arm2


UPDATE TBL_Arm2
SET Arm1_ID = A.ID
FROM TBL_ARM1 A
WHERE A.Title = Arm_Title