How to use the DATE_SUB function to perform subtraction on dates in MySQL

How to use the DATE_SUB function in MySQL to perform subtraction operations on dates

Introduction:
In the MySQL database, the DATE_SUB function is a function used to perform subtraction operations on dates. This function can easily implement subtraction operations on dates, such as calculating the date of a certain day in the past, calculating the date of a period of time ago, etc.

Usage:
The syntax of the DATE_SUB function is as follows:
DATE_SUB(date, INTERVAL expr unit)

Parameter description:

• date: required The date on which the subtraction operation was performed. It can be a specific date or a date and time field;
• expr: the value to be subtracted. It can be an integer or a numerical field;
• unit: the unit to be subtracted. It can be YEAR, QUARTER, MONTH, WEEK, DAY, HOUR, MINUTE, SECOND and other units;

Code examples:
The following are several specific examples of using the DATE_SUB function for subtraction operations.

1. Calculate the date of a certain day in the past:
   Assume that the current date is 2021-09-15, and we want to calculate the date 5 days ago. You can use the following code:

   SELECT DATE_SUB('2021-09-15', INTERVAL 5 DAY);

   The running result is: 2021-09-10, which is the date 5 days before the current date.

2. Calculate the date some time ago:
   Suppose we want to calculate the date and time 30 minutes ago. You can use the following code:

   SELECT DATE_SUB(NOW(), INTERVAL 30 MINUTE);

   The running result is the date and time 30 minutes before the current date and time.

3. Calculate the date some time ago:
   Suppose we have an order table, in which there is a field that is the order creation time created_at. We want to query orders created a month ago. You can use the following code:

   SELECT * FROM orders WHERE created_at < DATE_SUB(NOW(), INTERVAL 1 MONTH);

   This query will return all orders created one month ago.

Summary:
In the MySQL database, the DATE_SUB function is a very useful function that can perform subtraction operations on dates. By flexibly using the DATE_SUB function, various operations and calculations on dates can be realized, improving the flexibility and accuracy of data queries.

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