mysql的常用函数

2024/11/30 10:38:29 来源：https://blog.csdn.net/qq_35693377/article/details/140291856 浏览: 次关键词：mysql的常用函数

String

select concat(c1,’ ',c2);
SELECT CONCAT(first_name, ’ ', last_name) AS full_name FROM users;

select substring(c1,1,3);

length()
SELECT username FROM users WHERE LENGTH(username) < 5;

Math

round(num,3)四舍五入

select a1.machine_id ,round(avg(a2.timestamp - a1.timestamp),3) processing_time
from Activity a1
left join Activity a2 on
a1.machine_id = a2.machine_id and
a1.process_id = a2.process_id and
a1.activity_type = ‘start’ and
a2.activity_type = ‘end’
group by machine_id

date

datediff（c1,c2）；

SELECT DATEDIFF(NOW(), ‘2024-01-01’) AS days_since_new_year;

SELECT order_id, order_date, delivery_date
FROM orders
WHERE DATEDIFF(delivery_date, order_date) > 30;
DATEDIFF() 函数返回 date1 和 date2 之间的天数差。请注意，date1 和 date2 的顺序会影响结果的正负值。