各位大虾，求教！关于oracle的decode

Question

select 
decode(trim(A.TERM),'',A.TERM,decode(trunc(trim(A.TERM)/30),0,trim(A.TERM)||'D',trunc(trim(A.TERM)/30)||'M'||mod(trim(A.TERM),30)||'D'))
from A
这个语句，为什么字段A.TERM存在空时，会报错ORA-01722：无效数字？有什么办法解决吗？先行谢过！

Answer 1

--經測沒錯，應不是空引起的
SQL> create table A(TERM varchar2(20));已建立表格.SQL> insert into A values(null);已建立 1 個資料列.SQL> insert into A values('');已建立 1 個資料列.SQL> select trunc(trim('')/30) from dual;TRUNC(TRIM('')/30)                                                              
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Answer 2

--應貼這個
SQL> select
  2  decode(trim(A.TERM),'',A.TERM,decode(trunc(trim(A.TERM)/30),
  3  0,trim(A.TERM)||'D',trunc(trim(A.TERM)/30)||'M'||mod(trim(A.TERM),30)||'D'))
  4  from A
  5  ;DECODE(TRIM(A.TERM),'',A.TERM,DECODE(TRUNC(TRIM(A.TERM)/30),0,TRIM(A.TERM)||'D',
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