sql query with default value

CREATE TABLE TBL_EMPLOYEES(
	EMPLOYEE_ID INT NOT NULL IDENTITY
	, NAME VARCHAR(300)
	, JOB VARCHAR(50)
	, COMISSION FLOAT
	, CONSTRAINT PK_EMPLOYEE PRIMARY KEY (EMPLOYEE_ID)
)

when you run the data selection is obtained

SELECT * FROM TBL_EMPLOYEES

EMPLOYEE_ID	NAME	JOB	       COMISSION
1	        JOHN	MANAGER	   NULL
2	        CLARK	SALES	   NULL

SELECT 
EMPLOYEE_ID
, NAME
, JOB
, CASE 
	WHEN JOB = 'MANAGER' THEN 1000
	ELSE COMISSION	
	END COMISSION
FROM TBL_EMPLOYEES

EMPLOYEE_ID	NAME	JOB	       COMISSION
1	        JOHN	MANAGER	   1000
2	        CLARK	SALES	   NULL