일자별/월별/연도별 판매액 데이터를 확인해야하는 상황
1) 일별 판매액 확인
-- 일별 판매액 산출
SELECT * from olist_sales;
-- 날짜 가공
SELECT SUBSTR(order_purchase_timestamp,1,10) AS day, round(sum(payment_value)) AS sales
from olist_sales
GROUP BY day
ORDER BY day desc
INTO OUTFILE 'C:\\ProgramData\\MySQL\\MySQL Server 8.0\\Uploads\\olist_sales_daily.csv'
FIELDS TERMINATED BY ','
LINES TERMINATED BY '\n'
;

2) 월별 판매액 확인
-- 월별 판매액 산출
SELECT * from olist_sales;
-- 날짜 가공
SELECT SUBSTR(order_purchase_timestamp,1,7) AS month, round(sum(payment_value)) AS sales
from olist_sales
GROUP BY month
ORDER BY month desc
;

3) 연도별 판매액 확인
-- 연도별 판매액 산출
SELECT * from olist_sales;
-- 날짜 가공
SELECT SUBSTR(order_purchase_timestamp,1,4) AS year, round(sum(payment_value)) AS sales
from olist_sales
GROUP BY year
ORDER BY year desc
;

4) 요일별 판매액 확인
-- 요일별 판매액 산출
SELECT DAYNAME(order_purchase_timestamp) AS dayName, round(SUM(payment_value)) AS sales
FROM olist_sales
GROUP BY dayName
ORDER BY
CASE
WHEN dayName = 'Monday' THEN 1
WHEN dayName = 'Tuesday' THEN 2
WHEN dayName = 'Wednesday' THEN 3
WHEN dayName = 'Thursday' THEN 4
WHEN dayName = 'Friday' THEN 5
WHEN dayName = 'Saturday' THEN 6
WHEN dayName = 'Sunday' THEN 7
END ASC
;

SUBSTR함수를 활용하여 일별/월별/연도별 판매액을 각각 확인할 수 있었다.