MySQL INTERVAL Keyword Guidelines

在本教程中,我们将了解 MySQL INTERVAL Keywords and their values ​​to perform operations on date and time arithmetic.那么,让我们开始吧！

另请阅读：MySQL 中的 While 循环 – 完整参考

MySQL INTERVAL 简介

在 MySQL 中,INTERVAL Keywords are used to add or subtract date and time values.例如,If you want to add five days to the current day and display the new date,您可以使用 INTERVAL 关键字.

MySQL gives us a bunch of interval values.We'll see a full list of these interval values ​​below.

但首先,让我们看看如何使用 interval 关键字.

INTERVAL exp UNIT;

这里,exp 表示表达式,例如 1、2、100、200 or other unit-dependent expressions.Units are the units of measure in which dates and times are calculated,如日、时、分、秒等.

在上面的语法中,INTERVAL Both keywords and unit names are case-insensitive.

We can add or subtract interval values,如下所示 -

date + INTERVAL exp UNIT
date - INTERVAL exp UNIT

请注意,The date you specify must be in a valid datetime format.

Interval values ​​can also be used with other datetime functions,例如 ADDDATE()、DATE_ADD()、DATE_SUB()、TIMESTAMPDIFF() 等.

Format of expressions and units

下表显示了 exp 和 UNIT 的标准格式 -

Unit	exp
DAY	DAYS
DAY_HOUR	DAYS HOURS
DAY_MICROSECOND	DAYS HOURS:MINUTES:SECONDS.MICROSECONDS
DAY_MINUTE	DAYS HOURS:MINUTES
DAY_SECOND	DAYS HOURS:MINUTES:SECONDS
HOUR	HOURS
HOUR_MICROSECOND	HOURS:MINUTES:SECONDS.MICROSECONDS
HOUR_MINUTE	HOURS:MINUTES
HOUR_SECOND	HOURS:MINUTES:SECONDS
MICROSECOND	MICROSECONDS
MINUTE	MINUTES
MINUTE_MICROSECOND	MINUTES:SECONDS.MICROSECONDS
MINUTE_SECOND	MINUTES:SECONDS
MONTH	MONTHS
QUARTER	QUARTERS
SECOND	SECONDS
SECOND_MICROSECOND	‘SECONDS.MICROSECONDS’
WEEK	WEEKS
YEAR	YEARS
YEAR_MONTH	‘YEARS-MONTHS’

MySQL INTERVAL 示例

在第一个示例中,We'll add it for the current date 1 天.当前日期是 2022-07-05 (YYYY-MM-DD),So the output must be 2022-07-06.

SELECT CURDATE() + INTERVAL 1 DAY;

Add day interval

You can also subtract intervals from dates.此外,You can also specify your own date and time,But it must be in a valid datetime format.Check the example below -

SELECT '2022-01-01' - INTERVAL 1 DAY;

在这里,We specify the first day of the year,and try to subtract from it 1 天.The output should contain the previous year.让我们看看输出.

 

Subtract the day interval

如您所见,We got the expected output.

Let's see how to use interval values ​​with other datetime functions.

SELECT DATE_ADD('2022-01-01',INTERVAL 10 DAY);
SELECT DATE_SUB('2022-01-01',INTERVAL 10 DAY);

在这里,我们使用了 DATE_ADD() 和 DATE_SUB() Function to add and subtract interval values ​​for specified dates.

让我们看看输出.

Date addition and date sub-functions

正如你在这里看到的,We got the correct output.

MySQL INTERVAL 实例

Now we'll see some practical examples of using interval values.

We will create a form,In it we will store the member's data along with their registration date and membership expiry date.

我们将使用 DATE_ADD() The function calculates the expiration date.

CREATE TABLE members(
id INT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(100),
reg_date DATE DEFAULT(CURDATE()),
exp_date DATE DEFAULT(DATE_ADD(reg_date,INTERVAL 1 YEAR))
);

这里,在注册时,MySQL 会将 reg_date The value of the column is set to the current date.According to the registration date,The due date will be calculated.Let's try to insert the value and check if the due date column is getting the correct value.为此,We will explicitly insert some registration dates.

INSERT INTO members(name) VALUES ("Bob"),("Vilas"),("John");
INSERT INTO members(reg_date,name) VALUES ('2022-08-01',"Adam"),('2022-08-04',"Cetty");

Let's check the output.

SELECT * FROM members;

interval instance

如您所见,The expiration date is set after the registration date 1 年.

概括

在本教程中,我们了解了 interval 关键字及其值.注意,The range is wide.You can use it for different purposes,For example lookups will be in the future 10 Students who complete the course within days、A list of members whose membership will expire next month, etc.练习！