mysql惯用的日期函数汇总
mysql常用的日期函数汇总 最近做统计时经常用到的几个mysql函数: 1. UNIX_TIMESTAMP()? 该函数返回1970到现在的秒数,括号内也可以带参数,即返回1970年到指定时间段的秒数,注意是秒数,常用java的兄弟们需要注意,因为java中的System.currentTimeMillis()
mysql常用的日期函数汇总最近做统计时经常用到的几个mysql函数:
1. UNIX_TIMESTAMP()?
该函数返回1970到现在的秒数,括号内也可以带参数,即返回1970年到指定时间段的秒数,注意是秒数,常用java的兄弟们需要注意,因为java中的System.currentTimeMillis()返回的是毫秒数
?
2. date_format()
举一个例子 date_format(now(), '%Y-%m-%d %H:%i:%s') 将当前时间转换成某种时间格式的字符串,当然now()函数的默认格式已经是 '%Y-%m-%d %H:%i:%s'
?
3. FROM_UNIXTIME()
FROM_UNIXTIME(1390357150,'%Y-%m-%d'); 将返回1970年到指定时间段的秒数,转换成固定的时间格式,
这个适用于后台日期存放的是秒数,前台展示时需要的是具体的某种日期的应用
?
4. current_date()
这个函数的作用是返回当前的日期,但是这个函数在日期做减法时是会有Bug的,
以今天为例:
select current_date();
2014-01-24 |
我想知道今天以前的30天的日期
select current_date()-30;
20140094 |
显然不是我们想得到的值,经过测试发现当涉及到月份或年份的退位进位时就会出错
对于求今天之前的三十天,可以利用毫秒数做
select FROM_UNIXTIME(UNIX_TIMESTAMP(current_date())-24*60*60*30,'%Y-%m-%d');
哪位大神有更好的方法,欢迎指导
?
利用以上函数,就可以做简单的基于在线数量的统计,
相关表
? user_online_count_tbl
相关字段
? user_online_num(当前用户在线数)
? online_statistic_time(统计在线数时的时间)
?
?
5.基于最近10天的平均在线用户数统计
select sum(user_online_num)/count(online_statistic_time) as "avg_online_num", FROM_UNIXTIME(online_statistic_time,'%Y-%m-%d') as "dayTime" from user_online_count_tbl where FROM_UNIXTIME(online_statistic_time,'%Y-%m-%d') = FROM_UNIXTIME(UNIX_TIMESTAMP(current_date())-24*60*60*10,'%Y-%m-%d') group by FROM_UNIXTIME(online_statistic_time,'%Y-%m-%d')
?
?

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics



You can open phpMyAdmin through the following steps: 1. Log in to the website control panel; 2. Find and click the phpMyAdmin icon; 3. Enter MySQL credentials; 4. Click "Login".

MySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.

Redis uses a single threaded architecture to provide high performance, simplicity, and consistency. It utilizes I/O multiplexing, event loops, non-blocking I/O, and shared memory to improve concurrency, but with limitations of concurrency limitations, single point of failure, and unsuitable for write-intensive workloads.

MySQL's position in databases and programming is very important. It is an open source relational database management system that is widely used in various application scenarios. 1) MySQL provides efficient data storage, organization and retrieval functions, supporting Web, mobile and enterprise-level systems. 2) It uses a client-server architecture, supports multiple storage engines and index optimization. 3) Basic usages include creating tables and inserting data, and advanced usages involve multi-table JOINs and complex queries. 4) Frequently asked questions such as SQL syntax errors and performance issues can be debugged through the EXPLAIN command and slow query log. 5) Performance optimization methods include rational use of indexes, optimized query and use of caches. Best practices include using transactions and PreparedStatemen

MySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.

Effective monitoring of Redis databases is critical to maintaining optimal performance, identifying potential bottlenecks, and ensuring overall system reliability. Redis Exporter Service is a powerful utility designed to monitor Redis databases using Prometheus. This tutorial will guide you through the complete setup and configuration of Redis Exporter Service, ensuring you seamlessly build monitoring solutions. By studying this tutorial, you will achieve fully operational monitoring settings

The methods for viewing SQL database errors are: 1. View error messages directly; 2. Use SHOW ERRORS and SHOW WARNINGS commands; 3. Access the error log; 4. Use error codes to find the cause of the error; 5. Check the database connection and query syntax; 6. Use debugging tools.

Apache connects to a database requires the following steps: Install the database driver. Configure the web.xml file to create a connection pool. Create a JDBC data source and specify the connection settings. Use the JDBC API to access the database from Java code, including getting connections, creating statements, binding parameters, executing queries or updates, and processing results.
