Sql substring Function in oracle

Substr: The oracle substr function allows you to extract a substring .
The syntax for the oracle substr is as follows:-
substr(string,start_position,[ length])


SQL>  select substr('santosh chaurasia',2,6) from dual;

SUBSTR
------
antosh

sql> select substr('priyaseth',4) from dual;
SUBSTR
------
antosh

SQL> select substr('avinashkare',-4) from dual;
SQL> select instr('nikita_sharma','k') from dual;

INSTR('NIKITA_SHARMA','K')
--------------------------
                         3
SQL> select instr('america','e') from dual;
The instr function in sql used to find the starting locatin of a pattern in a string.
The syntax for instr(str) is as follows.
instr(str,pattern,[starting position,[nth locatin]])

INSTR('AMERICA','E')
--------------------
                   3
SQL>  select instr('nikitasony','n',2) from dual;-- for 2nd occurance

INSTR('NIKITASONY','N',2)
-------------------------
                        9
SQL> select lpad('vikram',10,'*') from dual;

LPAD('VIKR
----------
****vikram

SQL> select rpad('nasim',10,'*') from dual;

RPAD('NASI
----------
nasim*****



Trim :- Removes leading and /or trailing blanks(or other characters ) from a string.
Syntax:- TRim([[<trim_spec >] char ]

SQL> select trim('    Aptech Computer') from dual;


Returns the following result.

TRIM('APTECHCOM
---------------
Aptech Computer


Concate Function:-- 

The syntax for the oracle concat function is :
concat(string1,string2)

Parameters Or Arguments.

String1 is the first string to concatenate.
string2 is second string to concatnate....

SQL> select concat(trim(' 'from'Nikita_sharma '),'Good Morning') from dual;

CONCAT(TRIM(''FROM'NIKITA
-------------------------
Nikita_sharmaGood Morning


Length
Syntax
Length(char)
{fn length(char)}
Returns the length in characters of the string argument char.if the char has the datatype CHAR ,the length includes all trailing blanks.
if a char is null ,it returns null.

SQL> select length('Australia') from dual;

LENGTH('AUSTRALIA')
-------------------
                  9


SQL> select concat(trim(' 'from'Nikita_sharma '),'Good Morning') from dual;

CONCAT(TRIM(''FROM'NIKITA
-------------------------

Nikita_sharmaGood Morning