[Mysql] DATEDIFF function

The DATEDIFF function returns the number of days between two dates

Syntax format

DATEDIFF(date1,date2)

Parameter description

date1: compare date 1

date2: compare date 2

The DATEDIFF function returns the calculation result of date1 - date2. The two parameters, date1 and date2, must be valid date or datetime values; if the parameters are passed datetime values, the DATEDIFF function only uses the date part for calculation and ignores it.Time part (only the date part of the value is involved in the calculation)

Example

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

The difference between the DATEDIFF function and the TIMESTAMPDIFF function

1. The DATEDIFF function is only used to return the number of days between two dates, and the TIMESTAMPDIFF function is used to return and calculate the time difference between the specified units of two dates (the specified unit can be years, quarters, months, weeks, days, hours, minutes, secondsetc.)

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2. The calculation method of the date difference is reversed

The syntax format of the DATEDIFF function: DATEDIFF(start,end)

DATEDIFF function returns the calculation result of start - end

The syntax format of the TIMESTAMPDIFF function: TIMESTAMPDIFF(DAY,start,end)

TIMESTAMPDIFF function returns the calculation result of end - start

-- -2SELECT DATEDIFF('2022-04-28', '2022-04-30');-- 2SELECT TIMESTAMPDIFF(DAY,'2022-04-28', '2022-04-30');

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3. If the time is in YYYY-MM-DD HH:MM:SS format, when calculating the difference in days, TIMESTAMPDIFF uses the 24-hour format, even if it is 23:59:59, it is not counted as a day, andDATEDIFF is the direct subtraction of the part of the intercepted date.Then the number of days calculated using the two functions is different at this time

-- -2SELECT DATEDIFF('2022-04-30 00:00:00','2022-04-28 23:59:59');-- 1SELECT TIMESTAMPDIFF(DAY,'2022-04-28 23:59:59', '2022-04-30 00:00:00');

When the time format is YYYY-MM-DD HH:MM:SS, the results of using the two functions are different and need to be selected according to specific business scenarios

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Extended Supplement: TIMESTAMPDIFF Function

Exercise examples

Import data

DROP TABLE IF EXISTS coupon_collection;CREATE TABLE coupon_collection(user_id VARCHAR(8),collection_date DATE)ENGINE=InnoDBDEFAULT CHARSET = utf8;INSERT INTOcoupon_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=InnoDBDEFAULT CHARSET = utf8;INSERT INTOconsumption_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');

coupon_collection form (e-commerce coupon collection form)

user_id: User ID (VARCHAR type) collection_date: Date of coupon collection (DATE type)

consumption_info table (e-commerce consumption table)

user_id: User ID (VARCHAR type) consumption_date: Consumption date (DATE type)

Question: The coupons received by the user will take effect the next day, and will automatically take effect when shopping within the next 7 days, and the number of times of use is unlimited.It is required to obtain the users who have successfully used coupons to consume and their corresponding consumption times (output format: user_id, num)

user_id: The ID of the user who successfully used the coupon to consume num: The number of times of consumption

SELECT a.user_id, COUNT(collection_date)AS numFROM coupon_collection AS aINNER JOIN consumption_info AS bON a.user_id = b.user_idWHERE DATEDIFF(b.consumption_date,a.collection_date) BETWEEN 1 AND 7GROUP BY a.user_id;

Result display:

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