Oracle to_date，从mm/dd/yyyy到dd-mm-yyyy

Question

我将所有日期作为varchar2（10）插入到表中，并格式化为'mm/dd/yyyy'。我需要的是以下格式'mm-dd-yyyy'和日期数据类型。 没有PLSQL我的实现将是：

select day||'-'||month||'-'||year as formatted_date from 
(select 
extract(day from (select to_date('1/21/2000','mm/dd/yyyy') from dual)) as day, 
to_number(extract(month from (select to_date('1/21/2000','mm/dd/yyyy') from dual)),09) as month, 
extract(year from (select to_date('1/21/2000','mm/dd/yyyy') from dual)) as year 
from dual); 

结果是：21-1-2000而不是21-01-2000如预期。
当添加额外的TO_DATE（，）为：

to_date(day||'-'||month||'-'||year,'DD-MM-YYYY') as formatted_date 

它也不会更改日期和月份域海誓山盟。

Answer 1

我建议你在转换为字符串时使用TO_CHAR()。为了做到这一点，你需要先建立一个日期。

SELECT TO_CHAR(TO_DATE(DAY||'-'||MONTH||'-'||YEAR, 'dd-mm-yyyy'), 'dd-mm-yyyy') AS FORMATTED_DATE 
FROM 
    (SELECT EXTRACT(DAY FROM 
     (SELECT TO_DATE('1/21/2000', 'mm/dd/yyyy') 
     FROM DUAL 
     )) AS DAY, TO_NUMBER(EXTRACT(MONTH FROM 
     (SELECT TO_DATE('1/21/2000', 'mm/dd/yyyy') FROM DUAL 
     )), 09) AS MONTH, EXTRACT(YEAR FROM 
     (SELECT TO_DATE('1/21/2000', 'mm/dd/yyyy') FROM DUAL 
     )) AS YEAR 
    FROM DUAL 
    ); 

Answer 2

你不需要搞糟提取部分日期。只需使用to_date及其存储的格式将其转换为日期，然后将该日期转换为所需格式的字符。像这样：

select to_char(to_date('1/10/2011','mm/dd/yyyy'),'mm-dd-yyyy') from dual 

Answer 3

select to_char(to_date('1/21/2000','mm/dd/yyyy'),'dd-mm-yyyy') from dual