SQL Error: ORA-12899: value too large for column
ORA-12899: value too large for column "DJ"."CUSTOMERS"."ADDRESS" (actual: 25, maximum: 2
Tells you what the error is. Address can hold maximum of 20 characters, you are passing 25 characters.
As mentioned, the error message shows you the exact problem: you are passing 25 characters into a field set up to hold 20. You might also want to consider defining the columns a little more precisely. You can define whether the VARCHAR2 column will store a certain number of bytes or characters. You may encounter a problem in the future where you try to insert a multi byte character into the field, for example this is 5 characters in length but it won't fit into 5 bytes: 'ÀÈÌÕÛ'
Here is an example:
CREATE TABLE Customers(CustomerID VARCHAR2(9 BYTE), ...
or
CREATE TABLE Customers(CustomerID VARCHAR2(9 CHAR), ...
This answer still comes up high in the list for ORA-12899 and lot of non helpful comments above, even if they are old. The most helpful comment was #4 for any professional trying to find out why they are getting this when loading data.
Some characters are more than 1 byte in length, especially true on SQL Server. And what might fit in a varchar(20) in SQLServer won't fit into a similar varchar2(20) in Oracle.
I ran across this error yesterday with SSIS loading an Oracle database with the Attunity drivers and thought I would save folks some time.