Oracle Instr

四组例子，应该已经完全地说明用法了。

INSTR(源字符串, 目标字符串, 起始位置, 匹配序号)

SQL> SELECT INSTR('12_34_56_78', '_', 1, 1) As INSTR FROM DUAL;

     INSTR
----------
         3

SQL> SELECT INSTR('12_34_56_78', '_', -1, 1) As INSTR FROM DUAL;

     INSTR
----------
         9

SQL> SELECT INSTR('12_34_56_78', '_', 1, 2) As INSTR FROM DUAL;

     INSTR
----------
         6

SQL> SELECT INSTR('12_34_56_78', '_', -1, 2) As INSTR FROM DUAL;

     INSTR
----------
         6

SQL> SELECT INSTR('12_34_56_78', '_', 1, 3) As INSTR FROM DUAL;

     INSTR
----------
         9

SQL> SELECT INSTR('12_34_56_78', '_', -1, 3) As INSTR FROM DUAL;

     INSTR
----------
         3

SQL> SELECT INSTR('12_34_56_78', '_', 4, 1) As INSTR FROM DUAL;

     INSTR
----------
         6

SQL> SELECT INSTR('12_34_56_78', '_', -4, 1) As INSTR FROM DUAL;

     INSTR
----------
         6