Solved: “ORA-06502: PL/SQL: numeric or value error: character string buffer too small”

If you store a large text data as a CLOB data type in your Oracle database, you may come across to the error messages below when you query your table:

ORA-06502: numeric or value error: character string buffer too small
ORA-01489: result of string concatenation is too long

Background

CLOB data type is used to store large text data (up to 2 GB in MySQL and up to 128 TB in Oracle). Similarly, BLOB data type is used to store large binary data (videos, images, documents).

If you want to retrieve data from a CLOB field, you should convert data to a string data type. VARCHAR2 is commonly used string data type. However, it has a limitation of 4000 characters.

In my case, I use the following query to retrieve the data. Since I am requesting 5000 characters and VARCHAR2 only supports 4000, I receive the errors above.

select dbms_lob.substr(column1,5000,1)
from DIM_SW_TEST;

Solution

Write the same column name twice in the same SELECT query. So basically you divide the content in two VARCHAR2 fields (total of up to 8000 characters). Make sure to increase the buffer size with the SET BUFFER parameter.

set buffer 10000;
select dbms_lob.substr(column1,4000,1),
dbms_lob.substr(column1,4000,4001)
from DIM_SW_TEST;