introduction
In the fields of database management and data analysis, date-time functions and system functions are important tools for processing time series data, obtaining system information, and optimizing database operations. As a leading enterprise-level database system in China, Dameng Database provides rich date and time processing and system information acquisition functions. This article will introduce in detail several key date and time functions and system functions in the Dameng database, and analyze their usage through actual SQL examples to help you better utilize these functions to improve work efficiency.
1. Date and time function
1. CURRENT_DATE
Function: Return to the current date.
Example：
SELECT CURRENT_DATE;
2. CURRENT_TIME
Function: Returns the current time (excluding the date part).
Example：
SELECT CURRENT_TIME;
3. CURRENT_TIMESTAMP
Function: Returns the current date and time.
Example：
SELECT CURRENT_TIMESTAMP;
4. DATE_FORMAT
Function: Format date or date time according to the specified format.
Example：
SELECT DATE_FORMAT(CURRENT_TIMESTAMP, '%Y-%m-%d %H:%i:%s') AS formatted_time;
5. DATE_ADD
Function: Adds the specified time interval to the date.
Example: Calculate the date after one week.
SELECT DATE_ADD('DAY', 7, CURRENT_DATE) AS one_week_later;
6. DATEDIFF
Function: Calculate the time difference between two dates.
Example: Calculate the difference in the number of days during the two order days.
SELECT DATEDIFF('DAY', order_date, delivery_date) AS days_to_delivery
FROM orders;
2. System functions
1. USER
Function: Returns the user name of the currently logged in to the database.
Example：
SELECT USER();
2. DATABASE()
Function: Returns the database name of the currently connected.
Example：
SELECT DATABASE();
3. VERSION()
Function: Obtain the version information of the database server.
Example：
SELECT VERSION();
4. SYSTEM_USER
Function: Returns the operating system user of the current database session.
Example：
SELECT SYSTEM_USER;
5. SESSION_ID()
Function: Returns the ID of the current database session.
Example：
SELECT SESSION_ID();
6. LAST_INSERT_ID()
Function: Get the automatic growth ID generated by the last insert operation.
Example：
INSERT INTO users (username) VALUES ('new_user');
SELECT LAST_INSERT_ID();Summarize
This is the article about the date and time functions of DM Dameng data and the usage of system functions. For more related contents of DM Dameng data, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!