MySql date and time: how to process and convert

MySql is a commonly used relational database management system that supports data storage and operations of multiple date and time types. This article will introduce how to process and convert date and time data in MySql.

1. Date and time types

MySql supports multiple date and time types, including DATE, TIME, DATETIME, TIMESTAMP, etc. The specific definitions of these types are as follows:

1. DATE: represents the date in the format of 'YYYY-MM-DD'. The valid range is '1000-01-01' to '9999-12-31'.
2. TIME: indicates time in the format of 'HH:MM:SS'. The valid range is '-838:59:59' to '838:59:59'.
3. DATETIME: Represents date and time in the format of 'YYYY-MM-DD HH:MM:SS'. The valid range is '1000-01-01 00:00:00' to '9999-12-31 23:59:59'.
4. TIMESTAMP: Represents date and time in the format of 'YYYY-MM-DD HH:MM:SS'. The valid range is '1970-01-01 00:00:01' to '2038-01-19 03:14:07'.

2. Date and time functions

MySql provides a variety of date and time functions for processing and converting date and time data. Commonly used functions include:

1. DATE_FORMAT(date,format): Format the date into the specified format. For example, to format '2022-08-25' as 'August 25, 2022', you can use the following statement: SELECT DATE_FORMAT('2022-08-25','%M %d, %Y').
2. DATE_ADD(date,INTERVAL expr unit): Add the specified time interval to the date. For example, to add '2022-08-25' to 3 months, you can use the following statement: SELECT DATE_ADD('2022-08-25', INTERVAL 3 MONTH).
3. DATE_SUB(date,INTERVAL expr unit): Subtract the specified time interval from the date.
4. DATEDIFF(date1,date2): Calculate the difference in days between two dates. For example, to calculate the difference in days between '2022-08-01' and '2022-08-25', you can use the following statement: SELECT DATEDIFF('2022-08-25','2022-08-01').
5. DAYOFWEEK(date): Returns the day of the week corresponding to the date. For example, to return the day of the week corresponding to '2022-08-25', you can use the following statement: SELECT DAYOFWEEK('2022-08-25').
6. WEEK(date[,mode]): Returns the week number of the date. The mode parameter is used to specify the starting date of the week, which can be a value from 0 (indicating Sunday) to 7 (indicating Saturday). The default value is 0.
7. NOW(): Returns the current date and time.
8. TIMESTAMPDIFF(unit,start,end): Calculate the time difference between two dates in the specified unit. For example, to calculate the difference in months between '2022-01-01' and '2022-08-25', you can use the following statement: SELECT TIMESTAMPDIFF(MONTH,'2022-01-01','2022-08-25' ).
9. FROM_UNIXTIME(unix_timestamp[,format]): Convert Unix timestamp to the specified date and time format. For example, to convert Unix timestamp 1234567890 to 'YYYY-MM-DD HH:MM:SS' format, you can use the following statement: SELECT FROM_UNIXTIME(1234567890,'%Y-%m-%d %H:%i:%s ').

3. Date and time conversion

In MySql, you can use the STR_TO_DATE and DATE_FORMAT functions to convert date and time. STR_TO_DATE can convert strings to date and time types, while DATE_FORMAT can convert date and time types to strings. For example, to convert the string '20220825' to a date type, you can use the following statement: SELECT STR_TO_DATE('20220825','%Y%m%d').

4. Notes

When using date and time data, you need to pay attention to the following matters:

1. The storage precision of time defaults to seconds, and you can modify the data by table definition to increase precision.
2. Date and time types are compared and sorted in the form of strings. Therefore, attention needs to be paid to format consistency to avoid unexpected errors.
3. When performing date and time calculations, you need to consider the influence of factors such as time zone and daylight saving time.

In short, mastering the processing and conversion skills of date and time in MySql can help us manage and analyze data more efficiently.

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