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Using datetime in MySQL

2022-06-12 04:19:00 【allway2】

MySQL Date time tutorial

In this tutorial , I will explain by example MySQL DATE and TIME function .

DATETIME Values used to store date and time . By default ,DATETIME Values range from 1000-01-01 00:00:00 To 9999-12-31 23:59:59. It USES 5 Bytes for storage .

DATETIME Grammar of form ：

YYYY-MM-DD HH:MM:SS

MySQL Date and time type

MySQL There are many useful date and time functions in . I've seen too many applications perform date calculations at the code level , Instead, use the built-in MySQL Function can do the same . However , Before we start using these functions , Let's refresh our memory , have a look MySQL What date and time types can be used .

DATETIME	YYYY-MM-DD HH:MM:SS
DATE	YYYY-MM-DD
TIMESTAMP	YYYYMMDDHHSSMM
TIME	HH:MM:SS
YEAR	YYYY

MySQL Date time

MySQL Very loose in reading date format . Although it is wise to use conventions , But you can use any other punctuation you like . for example , Now create a table and insert the virtual data , As shown below .

CREATE TABLE vatsa(Dt DATETIME);

Now? , Insert data in the correct format , As shown below .

INSERT INTO vatsa(Dt) VALUES('2020-09-14 23:18:17');

note ：

You can use '=' and '+' Symbols instead of correct formatting , As shown below ：

INSERT INTO vatsa(Dt) VALUES('2020=09=14 23*18*21');

But even though I'm sure they exist , But I didn't find a good reason to use it , So I suggest you abide by the agreement , Unless absolutely necessary .

Now? , Execute the following query to view the results .

SELECT * FROM vatsa;

Simple date and time calculations

Date calculation is relatively easy . The first function we want to look at is YEAR() function , It returns the year of a given date . To get the year from the value 、 month 、 Zhou 、 Japan 、 quarter 、 date 、 Time 、 Hours 、 Minutes and seconds DATETIME value , Use the function shown in the following statement ：

for example ：

SELECT YEAR('2020-09-14 23:18:17') AS Year,  
    Month('2020-09-14 23:18:17') AS Month,  
    Day('2020-09-14 23:18:17') AS Day,  
    Hour('2020-09-14 23:18:17') AS Hour,  
    Minute('2020-09-14 23:18:17') AS Minute,  
    Second('2020-09-14 23:18:17') AS Second,  
    Date('2020-09-14 23:18:17') AS Date,  
    Time('2020-09-14 23:18:17') AS Time,  
    Quarter('2020-09-14 23:18:17') AS Quarter;

perhaps , Users can use dynamic methods to get the date and time of the current date and time .

SET @vatsaDATETIME = NOW();  
  
SELECT YEAR(@vatsaDATETIME) AS Year,  
    Month(@vatsaDATETIME) AS Month,  
    Day(@vatsaDATETIME) AS Day,  
    Hour(@vatsaDATETIME) AS Hour,  
    Minute(@vatsaDATETIME) AS Minute,  
    Second(@vatsaDATETIME) AS Second,  
    Date(@vatsaDATETIME) AS Date,  
    Time(@vatsaDATETIME) AS Time,  
    Quarter(@vatsaDATETIME) AS Quarter;

Basic arithmetic operation of date function

We can use “+” and “-” Operator performs a simple arithmetic operation on the date . Let's look at some basic examples .

for example ：

1） Find out which year is five years ahead of a given date , You can use it .

SET @vatsa = now();  
SELECT @vatsa + 5;

2) To find out what the last five years were , Please use .

SET @vatsa = now();  
SELECT @vatsa – 5;

Now? , Let's discuss a basic real-time example .

SET @vatsa = now();  
SELECT @vatsa - 5 AS PAST,  
    year(@vatsa) AS CURRENT,  
    @vatsa + 5 AS FUTURE;

NOW() function

Of course , You don't have to hard code the date .MySQL Very capable of telling the date and time , Use NOW() function . also , When executing this statement , It will return the current date and time .

SELECT NOW();

CURRENT_DATE() function

Or just use CURRENT_DATE() Date of function . also , When executing this statement , It will return the current date .

SELECT CURRENT_DATE();

MySQL Date time and timestamp

TIMESTMP Be similar to MySQL Medium DATTIME.TIMESTAMP need 4 Bytes , but DATETIME need 5 Bytes .

TIMESTAMP Columns store complete 14 Characters , But you can display it in different ways . for example , If the column is defined as TIMESTAMP(2), Only two digit years will be displayed , But the full value is stored . If you later decide to display the full value , You can change the table definition , The full value will appear .

Definitions are listed below TIMESTAMP And the results show that .