(Oracle DB) - 23. Expression

/* Expression
	#	Expression is combined with
									one or more perands
									And zero or more operators
									Or SQL functions. 
*/

/* CASE Expression */
CASE
	WHEN condition_1
		THEN value_1
	WHEN condition_2
		THEN value_2
	...
	ELSE value_etc
END column_name_of_results
	--	NOTE : Data type of result values (value_1, ..., value_etc) MUST BE same!


/* Test of CASE Expression
	employee중에서,
	salary가 5,000 이하라면 grade C
	salary가 5,000 초과 ~ 15,000 이하라면 grade B
	salary가 15,000 초과라면 grade A
	를 return하는 query를 작성해보자.		
*/

SELECT
	employee_id,
	salary,
	CASE
		WHEN salary <= 5000
			THEN 'C'
		WHEN salary > 5000 AND salary <= 15000
			THEN 'B'
		ELSE 'A'
	END salary_grade
	FROM employees
;