The eighth chapter of Mysql [commonly used functions]

Numeric function

Function name	Work
abs	Find the absolute value
sqrt	Find the square root
mod	Find the remainder
ceil 和 ceiling	Both functions have the same function, both return the smallest integer that is not less than the parameter, ie round up
floor	Round down, the return value is converted into a BIGINT
rand	Generate a random number between 0 and 1, the integer parameter is used to generate a repeating sequence
round	Round off the passed parameters
sign	Return the symbol of the parameter
pow and power	Both functions have the same function and are the result of the power of the passed parameter
without	Find the sine value
asin	Find the inverse sine value and inverse function with the function SIN
cos	Find the cosine
acos	Find the inverse cosine value and inverse function with the function COS
tan	Find the tangent
assign	Find the arc tangent value, which is an inverse function with the function TAN
cot	Find the cotangent

String functions

Function name	Work
length	Calculate string length function, return the length of the string in bytes
concat	Combine string functions, return the result is the string generated by the connection parameters
insert	Replace string function
lower	Convert letters in string to lower case
upper	Convert letters in a string to uppercase
left	Truncate the character string from the left word and return several characters to the left of the string
right	Intercept the character string from the right word and return several characters to the right of the string
trim	Delete the spaces on the left and right of the string
replace	String replacement function, returns the new string after replacement
substr 和 substring	Truncate the string, return the specified length of characters starting from the specified position
reverse	String reversal (reverse order) function, returns the string in reverse order from the original string

Date and time functions

Function name	Work
curdate 和 current_date	Both functions have the same effect, returning the date value of the current system
curtime 和 current_time	Both functions have the same effect and return the current system time value
now 和 sysdate	Both functions have the same effect, returning the date and time values ​​of the current system
unix_timestamp	Get UNIX timestamp function, returns an unsigned integer based on UNIX timestamp
from_unixtime	Convert UNIX timestamp to time format, inverse function with UNIX_TIMESTAMP
month	Get the month in the specified date
monthname	获取指定日期中的月份英文名称
dayname	获取指定曰期对应的星期几的英文名称
dayofweek	获取指定日期是一周中是第几天，返回值范围是1~7,1=周日
week	获取指定日期是一年中的第几周，返回值的范围是否为 0〜52 或 1〜53
dayofyear	获取指定曰期是一年中的第几天，返回值范围是1~366
dayofmonth	获取指定日期是一个月中是第几天，返回值范围是1~31
year	获取年份，返回值范围是 1970〜2069
time_to_sec	将时间参数转换为秒数
sec_to_time	将秒数转换为时间，与TIME_TO_SEC 互为反函数
date_add 和 adddate	两个函数功能相同，都是向日期添加指定的时间间隔
date_sub 和 subdate	两个函数功能相同，都是向日期减去指定的时间间隔
addtime	时间加法运算，在原始时间上添加指定的时间
subtime	时间减法运算，在原始时间上减去指定的时间
datediff	获取两个日期之间间隔，返回参数 1 减去参数 2 的值
date_format	格式化指定的日期，根据参数返回指定格式的值
weekday	获取指定日期在一周内的对应的工作日索引

流程控制函数

函数名称	作用
if	判断，流程控制
ifnull	判断是否为空
case	搜索语句

聚合函数

函数名称	作用
max	查询指定列的最大值
min	查询指定列的最小值
count	统计查询结果的行数
sum	求和，返回指定列的总和
avg	求平均值，返回指定列数据的平均值

其它函数

函数名称	作用
version	数据库版本号
database	当前的数据库
user	当前连接用户
md5	返回字符串的md5数据