常用系统函数

select GETDATE() as 当前时间; --获取当前时间

select
len('张三') as 长度1,
len('Hello sql') as 长度2; --获取字符串长度

--案例

create table testName(name varchar(20));
insert into testName values('刘德华'),('李白');

select name,len(name) as 字符长度
from testName;

--截取字符串
--从第一位开始 截3个字符
select SUBSTRING('abcdefgh',1,3) as 结果1;

select SUBSTRING('abcdefgh',4,2) as 结果2;

--案例
select
SUBSTRING('138001138000',1,3) +'****'+substring('13800138000',8,4)
as 隐藏手机号;

--字符串替换
select REPLACE('百度很好用','百度','字节') as 替换结果;

--去掉所有空格
select REPLACE('2026-05-04 12:30',' ','') as 去空格;

select CONVERT(nvarchar(10),GETDATE(),120) as 年月日;

select CONVERT(varchar(10),GETDATE(),101) as 月日年;

select CONVERT(varchar(10),12345) as 数字转文本;