017 数据库学习笔记--常用函数

select NEWID() as GUID
select GETDATE() as 日期
go

--month()函数当前月时，不足10的前面补0
select '0'  + convert(varchar(2),month(getdate()))
--不满10补领——获取到月份 + 100 ，再获取后两位，即可获取到月份
Select Right(100 + Month(GETDATE()), 2)
select  convert(int,month(getdate()))

--打印月份
declare @month int 
set @month=convert(int,month(getdate()))
--------------if
if @month <10
begin 
	print( '0'  + convert(varchar(2),month(getdate())))
end
--------------else
else 
begin 
	print(convert(varchar(2),month(getdate())))
end


go
--返回字符串中指定的子串出现的开始位置(索引从1开始)
select charindex('34','1234567890123') as startIndex
--返回字符串中指定的子串出现的开始位置(索引从1开始，字串前必须加%)
select patindex('%34%','1234567890123') as startIndex

--大小写转化
select lower('abc') 小写,upper('abc') 大写

--去空格;	LTRIM去除左侧空格;		RTRIM去除左侧空格  
select LTRIM(' abc  ') 去除左侧空格,RTRIM('  abc   ') 去除右侧空格

--截取字符串 retrun 1234
select LEFT('123456',4) as 从左侧开始截取截取4位 --return1234
select RIGHT('123456',4) as 从左侧开始截取截取4位 --return3456
--获取字符串长度
select len('helloWpf') as strLength
select datalength('helloWpf') as strLength
--获取数据库名称
select db_name() as 当前数据库名称

--类型转换
select 1+2 as sumno --retrun 3
select '1' + '2' as sumno --return 12
select 'a' +'b' as ab --return ab
select 'abc' + convert(varchar,2) as abc2 --return asc ,注： 字符串和数字拼接时，需对数字进行类型转换，否则将报错

select convert(varchar,2.21) FloatToString
select convert(varchar,2)  IntToString 
select convert(varchar(10),getdate(),21)  DateToString --(yyyy-MM-dd)  23 表示日期格式，有多种方式

--int to decimal or decimal
SELECT cast('123' AS float),cast('456.233' AS decimal(18,2))
--string to datetime
select cast('2012-11-11'as datetime) as StringToDatetimeByCast
--datetime to varchar  无法指定日期格式
select cast(getdate() as varchar)

--复制字符串2次
select replicate('I love you ',2) as 复制字符串2次
select reverse (110) as 翻转字符串

--判断表达式内容是否为数字或是否可转为数字(1--表示数字，0--表示非数字)
select isnumeric(100)数字,isnumeric('100')可转为数字,isnumeric('abc')字母

--row_number  编号或说是排序函数
select row_number() over(order by student_name desc) as orderno from student

--聚合函数count 、max、min、sum、avg
select count(*) from student
select count(1) from student -- 建议使用
select max(student_age) maxage from student
select min(student_age) minage from student
select sum(student_age) sumage from student
select avg(student_age) avgage from student

截取小数：

------------------------截取两位小数------------------------
select cast('123.1212' AS float)
select cast('456.2355' AS decimal(18,2))
select round((CONVERT(FLOAT,'456.2355')),2)
select cast('123.1212' AS float)as count1,cast('456.2355' AS decimal(18,2))as count2,round((CONVERT(FLOAT,'456.2355')),2)as count3 
------------------------截取两位小数------------------------

case left：

select  case when  LEFT('-123456',1) ='-' then '-123456'
		     when  LEFT('-123456',1) <>'-' then '123456' end  as "test"

str函数：

--STR()函数将包含4位数和小数点的数字转换为具有两个小数位的4位字符串
--参数1为原始数据
--参数2为返回值位数，例如6位数、5位数
--参数3，表示小数点后位数，例如2(位数不够则不显示)
SELECT   STR(123.4567, 6, 2) result
SELECT   STR(123.45678, 5, 2) result

示例：

set @TableNameL=  select (lower(left(@TableName,1))+lower(SUBSTRING(@TableName,2,len(@TableName))) )

select (lower(left('abCdsE',1))+lower(SUBSTRING('abCdsE',2,len('abCdsE'))) )

select (lower(left('helloWpf',1))+SUBSTRING('helloWpf',2,len('helloWpf'))) 


----------------------大小写转化----------------------
select upper('helloWpf') as ToUpper,lower('helloWpf') as ToLower
go
--示例
declare @TableNameL varchar(200), @TableName sysname = 'DictPublic'
set @TableNameL = (select (lower(left('helloWpf',1))+SUBSTRING('helloWpf',2,len('helloWpf'))))
set @TableName = (select (lower(left(@TableName,1))+SUBSTRING(@TableName,2,len(@TableName))))
select @TableNameL as test1,@TableName as test2
print @TableNameL
print @TableName
go
----------------------大小写转化----------------------

select * from VIEW_APP_RESULT where 
APPOINTSDATE>='2020-01-25' and APPOINTSDATE<='2023-05-30'
and appkind='FSK'

exec sp_helpindex his_queue
go
exec sp_helpindex queuedetail