How to Avoid 'ORA-06502' Error When Querying Oracle CLOB Columns?

Querying CLOB Columns in Oracle: Handling 'ORA-06502' Error

When querying Oracle database tables containing CLOB (Character Large Object) columns, you may encounter situations where certain fields display only "(CLOB)" as their value instead of actual data. To retrieve the actual CLOB data, you can use the DBMS_LOB.substr() function.

However, using DBMS_LOB.substr() alone can sometimes result in the "ORA-06502: PL/SQL: numeric or value error: character string buffer too small" error, indicating that the specified buffer size is inadequate to store the CLOB data.

To resolve this issue, you can use the following approach:

select DBMS_LOB.substr(myColumn, 3000) from myTable

In this query, we explicitly specify the buffer size (3000) to be used by DBMS_LOB.substr(). This ensures that a sufficient buffer is allocated to accommodate the potential length of the CLOB data. You can adjust the buffer size as needed if necessary.

By using this technique, you can successfully query and retrieve the actual content of CLOB columns in Oracle, overcoming the limitations of the default "(CLOB)" value display.

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