MySQL: built-in function

https://dev.mysql.com/doc/refman/8.0/en/miscellaneous-functions.html

https://dev.mysql.com/doc/refman/8.0/en/built-in-function-reference.html

1. left(string,length)

   

    

2. substring(string,position,length)
   
   substring === substr

   ****** 从1计数
   

     

3. replace(string,old_str,new_str) 多字节安全
   

     

4. 日期减 date_sub
   

   select date_sub(now(),interval 3 day);

   

     

5.  

   日期加 date_add
   

   select date_add(current_timestamp(),interval 50 minute);