这很简单，但不漂亮。从数据类型转换列 NUMBER 至 VARCHAR2 用前导零填充，使用 fm 抑制任何空格 + 或者 - :

SELECT TO_CHAR(month,'fm00') FROM mytable;
05

接下来，将转换的列与 || 运算符获取单个长字符串：

SELECT TO_CHAR(year,'fm0000')||TO_CHAR(month,'fm00')|| ...
20200519...

这个长字符串现在可以转换为数据类型 DATE ，或者，在你的情况下 TIMESTAMP 因为你有毫秒。您需要指定使用的日期格式，f.i.“yyyymmdd…”

SELECT TO_TIMESTAMP(TO_CHAR(year,'fm0000')|| ... , 'YYYYMM')

完整的示例如下所示：

SELECT TO_TIMESTAMP(
         TO_CHAR(year,'fm0000')||TO_CHAR(month,'fm00')||
         TO_CHAR(day,'fm00')||TO_CHAR(hour24,'fm00')||
         TO_CHAR(minute,'fm00')||TO_CHAR(second,'fm00')||
         TO_CHAR(ms,'fm000')
         , 'YYYYMMDDHH24MISSFF3')
  FROM (-- your table, as a mockup, I'll use DUAL
        SELECT 2020 as year, 5 as month, 19 as day, 
               13 as hour24, 7 as minute, 10 as second, 
               300 as ms 
          FROM DUAL);

2020-05-19 13:07:10,300000000

编辑：
填充模式修改器 fm 抑制正数的前导空格（为 - 负数的符号）。日期的所有部分都是正数，所以字符串中有很多空格。

SELECT TO_CHAR(x,'99'), TO_CHAR(x,'fm99')
  FROM (SELECT -10 as x FROM DUAL UNION ALL SELECT 10 FROM DUAL);
| 10|10|
|-10|-10|

文档在格式模型修改器下有点隐藏。
想一想，不妨保留空格，调整格式模型：

SELECT TO_TIMESTAMP(
         TO_CHAR(year,'0000')||TO_CHAR(month,'00')||
         TO_CHAR(day,'00')||TO_CHAR(hour24,'00')||
         TO_CHAR(minute,'00')||TO_CHAR(second,'00')||
         TO_CHAR(ms,'000')
         ,' YYYY MM DD HH24 MI SS FF3')
  FROm (SELECT 2020 as year, 5 as month, 19 as day, 
                 13 as hour24, 7 as minute, 10 as second, 
                300 as ms FROM DUAL);