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MySQL函数
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概述
MySQL函数是MySQL数据库中的一种特殊的语法，用于对数据进行处理和计算，本文介绍了MySQL函数的基本语法和常用操作。
文本处理
| 函数 | 说明 | 示例 |
|---|---|---|
| UPPER | 将字符串转换为大写 | SELECT UPPER('hello') AS Uppercase; |
| LOWER | 将字符串转换为小写 | SELECT LOWER('WORLD') AS Lowercase; |
| LENGTH | 获取字符串的长度 | SELECT LENGTH('Moonshot') AS Length; |
| CONCAT | 拼接字符串 | SELECT CONCAT('Hello', ' ', 'World') AS ConcatenatedString; |
| SUBSTRING | 截取字符串 | SELECT SUBSTRING('Moonshot', 1, 5) AS Substring; |
| REPLACE | 替换字符串 | SELECT REPLACE('Moonshot', 'Moon', 'Star') AS ReplacedString; |
日期和时间处理
| 函数 | 说明 | 示例 |
|---|---|---|
| NOW | 获取当前日期和时间 | SELECT NOW() AS CurrentDateTime; |
| CURDATE | 获取当前日期 | SELECT CURDATE() AS CurrentDate; |
| CURTIME | 获取当前时间 | SELECT CURTIME() AS CurrentTime; |
| DATE | 获取日期部分 | SELECT DATE('2024-09-18 08:23:45') AS DatePart; |
| TIME | 获取时间部分 | SELECT TIME('2024-09-18 08:23:45') AS TimePart; |
| YEAR | 获取年份 | SELECT YEAR(CURDATE()) AS Year; |
| MONTH | 获取月份 | SELECT MONTH(CURDATE()) AS Month; |
| DAY | 获取天数 | SELECT DAY(CURDATE()) AS Day; |
| HOUR | 获取小时 | SELECT HOUR(CURTIME()) AS Hour; |
| MINUTE | 获取分钟 | SELECT MINUTE(CURTIME()) AS Minute; |
| SECOND | 获取秒数 | SELECT SECOND(CURTIME()) AS Second; |
| WEEKDAY | 获取星期 | SELECT WEEKDAY(CURDATE()) AS Weekday; |
| DAYOFYEAR | 获取年的第几天 | SELECT DAYOFYEAR(CURDATE()) AS DayOfYear; |
| WEEK | 获取年的第几周 | SELECT WEEK(CURDATE()) AS WeekOfYear; |
| DATEDIFF | 计算日期差 | SELECT DATEDIFF(CURDATE(), '2024-01-01') AS DateDifference; |
| DATE_FORMAT | 日期格式化 | SELECT DATE_FORMAT(CURDATE(), '%Y-%m-%d') AS DateFormat; |
| DATE_ADD | 日期加 | SELECT DATE_ADD(CURDATE(), INTERVAL 1 DAY) AS DateAdd; |
| DATE_SUB | 日期减 | SELECT DATE_SUB(CURDATE(), INTERVAL 1 DAY) AS DateSub; |
数值处理
| 函数 | 说明 | 示例 |
|---|---|---|
| ABS | 绝对值 | SELECT ABS(-10) AS AbsoluteValue; |
| CEIL | 向上取整 | SELECT CEIL(3.14) AS CeilValue; |
| FLOOR | 向下取整 | SELECT FLOOR(3.14) AS FloorValue; |
| ROUND | 四舍五入 | SELECT ROUND(3.14) AS RoundValue; |
| RAND | 随机数 | SELECT RAND() AS RandomNumber; |
| SQRT | 平方根 | SELECT SQRT(16) AS SquareRoot; |
| POW | 幂运算 | SELECT POW(2, 3) AS Power; |
| MOD | 取模运算 | SELECT MOD(10, 3) AS Modulus; |