Mysql中DATEDIFF函数的基础语法及练习案例

-- 1
SELECT DATEDIFF('2022-04-30','2022-04-29');
-- 0
SELECT DATEDIFF('2022-04-30','2022-04-30');
-- -1
SELECT DATEDIFF('2022-04-29','2022-04-30');
 
-- 0
SELECT DATEDIFF('2022-04-30','2022-04-30 14:00:00');
-- 1
SELECT DATEDIFF('2022-04-30 13:00:00','2022-04-29 14:00:00');
-- 10
SELECT DATEDIFF('2017-06-25 09:34:21', '2017-06-15');

DROP TABLE IF EXISTS coupon_collection; 
CREATE TABLE coupon_collection( 
user_id VARCHAR(8), 
collection_date DATE 
) 
ENGINE = InnoDB 
DEFAULT CHARSET = utf8; 
INSERT INTO 
coupon_collection (user_id,collection_date) 
VALUE ('u001','2021-05-01') 
 ,('u002','2021-05-01') 
 ,('u003','2021-05-02') 
 ,('u004','2021-05-02')
 ,('u005','2021-05-03'); 
 
DROP TABLE IF EXISTS consumption_info; 
CREATE TABLE consumption_info( 
user_id VARCHAR(8), 
consumption_date DATE 
) 
ENGINE = InnoDB 
DEFAULT CHARSET = utf8; 
INSERT INTO 
consumption_info (user_id,consumption_date) 
VALUE ('u002','2021-04-28') 
 ,('u001','2021-04-29') 
 ,('u001','2021-05-03') 
 ,('u003','2021-05-05') 
 ,('u005','2021-05-06') 
 ,('u001','2021-05-08') 
 ,('u004','2021-05-09') 
 ,('u006','2021-05-09') 
 ,('u003','2021-05-10') 
 ,('u002','2021-05-10');

SELECT a.user_id, COUNT(collection_date)AS num 
FROM coupon_collection AS a
INNER JOIN consumption_info AS b
ON a.user_id = b.user_id
WHERE DATEDIFF(b.consumption_date,a.collection_date) BETWEEN 1 AND 7
GROUP BY a.user_id;