Here is a summary of some of my notes during my study:
1.Replace replace when displayed
select replace(ename,'A','China') from emp;
2.Instr(c1,c2,I,J) find the position where the specified character appears
C1 original string C2 specified string I start The nth occurrence of the initial position J
Select instr('oracle traing','ra',1,2) from dual;(virtual table)
3.Ascii returns the ascii value of the string
Select ascii('A'),ascii(' a'),ascii('0') from dual;
4.Chr gives an integer and returns the character
Select chr(54740), chr(65) from dual;
5.Concat connection string has the same effect as ||
Select concat(ename ,'haha')from emp;
6.Initcap returns a string, and capitalizes the first character of the string, other lowercase
Select initcap(ename) from emp;
7.Length string length (Chinese characters only occupy 1 character size)
Select length（ename）from emp;
8.Lower lowercase all characters
Select lower(ename)from emp;
9.Upper uppercase all characters
Select upper(ename)from emp;
10.Substr take a string
Select substr(‘aaasss’,2,4) from dual;