ORA-01843：不是有效的月份错误

Question

I have a column in Oracle DB which is varchar2 data type. Typical value stored in this column is like 06/16/2015 02:14:18 AM . I am trying to get all records wherein this column is having records after 1st August 2015.

select * 
from MYTABLE 
where to_date(substr(MYCOLUMN,1,10),'dd-mm-yyyy') > to_date('01-08-2015','dd-mm-yyyy');

But, I am getting ORA-01843 . Where am I doing wrong?

Answer 1

遵守VARCHAR中的格式

....where to_date(substr(MYCOLUMN,1,10),'mm/dd/yyyy')

Answer 2

I have a column in Oracle DB which is varchar2 data type. Typical value stored in this column is like 06/16/2015 02:14:18 AM.

The first question is why do you store DATE as string ? Using appropriate data type is one of the most important part of database design and performance .

Understand that DATE doesn't have the format you see, it is internally stored in 7 bytes which is Oracle's proprietary format. Storing date as a string to have a fixed format is not recommended.

I would suggest first fix the design so that you don't have to do this overhead activity while comparing dates . In the longer run it will help you.

1. Add a new column as DATE data type.

ALTER TABLE table_name 
   ADD new_column DATE;

2. Update the new column.

UPDATE table_name 
   SET new_column = TO_DATE(old_column, 'mm/dd/yyyy hh:mi:ss pm');

3. DROP the old column.

ALTER TABLE table_name 
   DROP COLUMN old_column;

4. Rename the new column to old column name.

ALTER TABLE table_name
  RENAME COLUMN old_name to new_name;

Now, you could compare dates easily:

SELECT * FROM MYTABLE WHERE mycolumn > to_date('01-08-2015','dd-mm-yyyy');

This will also use any regular index on the date column.

From performance point of view :

If you don't fix it now, you will keep facing performance issues. Because the immediate fix of SUBSTR will not let you use any regular index , you need to create a function-based index .

Answer 3

如果在表格中的所有值06/16/2015 02:14:18 AM ，那么你可以使用trunc(to_date(MYCOLUMN,'mm/dd/yyyy HH:mi:SS PM'),'dd')对to_date(substr(MYCOLUMN,1,10),'dd-mm-yyyy') 。