INSTR function is used to find position of string in search string from starting or ending point in Oracle

Syntax:

INSTR (string , substring [, position [, occurrence ] ])

Parameter 1: String is the value inwhich function look.
Parameter 2: Substring is the string value search in Parameter 1 String
Parameter 3: (Default 1 mention position return) If you use -1 then it will start from the end of the string.
Parameter 4: Occurrence used to find the position of 1st or 2nd or 3rd occurance.

Example: INST is used with different parameter to find the position

SQL> SELECT INSTR('THIS IS THE BEST THING','T',1) "Position" from dual;

Position
--------
       1

SQL> SELECT INSTR('THIS IS THE BEST THING','T',1,2) "Position" from dual;

Position
--------
       9

-- USe -1 third parameter, find position from backward.
SQL> SELECT INSTR('THIS IS THE BEST THING','T',-1) "Position" from dual;

Position
--------
      18

-- Use -1 third parameter indicate find position from backward 
SQL> SELECT INSTR('THIS IS THE BEST THING','T',-1,2) "Position" from dual;

Position
--------
      16

SQL> SELECT INSTR('THIS IS THE BEST THING','T',2) "Position" from dual;

Position
--------
       9

SQL> SELECT INSTR('THIS IS THE BEST THING','T',1,2) "Position Found" from dual;

Position
--------
       9