SQL> select substr('12345',1,3) from dual;SUB
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123SQL> select substr('12345',instr('12345','3')) from dual;SUB
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345SQL> select substr('12345',1,instr('12345','3')) from dual;SUB
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123
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123SQL> select substr('12345',instr('12345','3')) from dual;SUB
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345SQL> select substr('12345',1,instr('12345','3')) from dual;SUB
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123
SQL> select substr('1222',1,3) from dual;SUBSTR('1222',1,3)
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122
substr(character_expression,length(character_expression) - number_expression + 1, number_expression)比如取'abcde fgh'的最后三位:SQL> select substr('abcde fgh',length('abcde fgh') - 3 + 1, 3) from dual;SUBSTR('ABCDEFGH',LENGTH('ABC
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fgh