Oracle 支持的SQL中 用什么函数据把字符串转换成整型？？？

Question

select to_number(trim(to_char(datefiled,'hh'))) from dual

Answer 1

SQL> select to_number(to_char(sysdate-1.5,'hh24')) from dual;TO_NUMBER(TO_CHAR(SYSDATE-1.5,'HH24'))
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                                     4SQL> select to_number(to_char(sysdate,'hh24')) from dual;TO_NUMBER(TO_CHAR(SYSDATE,'HH24'))
----------------------------------
                                16SQL> declare
  2  num1 number(10):=0;
  3  num2 number(10):=0;
  4  begin
  5  select to_number(to_char(sysdate,'hh24')) into num1 from dual;
  6  select  to_number(to_char(sysdate-1.5,'hh24')) into num2 from dual;
  7  dbms_output.put_line(num1+num2);
  8  end;
  9  /
20PL/SQL procedure successfully completed.SQL>

Answer 2

SQL> select to_number(to_char(sysdate-1.5,'hh24')) from dual;TO_NUMBER(TO_CHAR(SYSDATE-1.5,'HH24'))
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                                     4SQL> select to_number(to_char(sysdate,'hh24')) from dual;TO_NUMBER(TO_CHAR(SYSDATE,'HH24'))
----------------------------------
                                16SQL> declare
  2  num1 number(10):=0;
  3  num2 number(10):=0;
  4  begin
  5  select to_number(to_char(sysdate,'hh24')) into num1 from dual;
  6  select  to_number(to_char(sysdate-1.5,'hh24')) into num2 from dual;
  7  dbms_output.put_line(num1+num2);
  8  end;
  9  /
20PL/SQL procedure successfully completed.SQL>

Answer 3

一般情况下oracle自动进行字符与整形的互相转换的
如：
SQL> select to_char(sysdate,'hh24')-10 from dual;TO_CHAR(SYSDATE,'HH24')-10
--------------------------
                         7已用时间:  00: 00: 00.40
SQL> select 24||'b' from dual;24|
---
24b已用时间:  00: 00: 00.50
SQL>

Answer 4

to_number(to_char(datefiled, 'hh'))

Answer 5

select to_char(datefiled, 'hh24') - 1 from dual;
 
TO_CHAR(SYSDATE,'HH24')-1
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                       9