DBMS_LOB.CONVERTTOBLOB is a procedure in Oracle Database provided by the DBMS_LOB package, which is a powerful and comprehensive set of APIs for managing large objects (LOBs) in Oracle databases. LOBs include Binary Large Objects (BLOBs), Character Large Objects (CLOBs), and National Character Large Objects (NCLOBs), among others. These are used to store large volumes of data such as texts, documents, multimedia content, etc.
The CONVERTTOBLOB procedure specifically is used to convert a character LOB (either a CLOB or NCLOB) into a binary LOB (BLOB). This conversion is particularly useful when you need to handle character data in a binary format, for example, for encryption, compression, or to prepare data for certain types of network transmission.
Syntax
The basic syntax for DBMS_LOB.CONVERTTOBLOB is as follows:
DBMS_LOB.CONVERTTOBLOB( dest_lob IN OUT NOCOPY BLOB, src_clob IN CLOB CHARACTER SET ANY_CS, amount IN INTEGER, dest_offset IN INTEGER DEFAULT 1, src_offset IN INTEGER DEFAULT 1, blob_csid IN INTEGER, lang_context IN OUT INTEGER, warning OUT INTEGER);
Parameters
dest_lob: The BLOB locator to which the CLOB or NCLOB data is to be converted and stored.
src_clob: The CLOB or NCLOB locator that points to the character data to be converted.
amount: The number of characters to convert.
dest_offset: The position in the destination BLOB where the converted data starts. The first position is 1.
src_offset: The position in the source CLOB/NCLOB from where to start the conversion. The first position is 1.
blob_csid: The character set ID of the destination BLOB. This is important for determining how character data is converted into binary format.
lang_context: A parameter used internally for character set conversion. Typically, it is initialized to the default value before the first call and passed to subsequent calls.
warning: An output parameter that flags any warnings. For example, if the conversion results in data truncation, a specific warning code is returned.
Usage Scenario
CONVERTTOBLOB is useful in scenarios where you have text data (CLOB/NCLOB) that needs to be processed or stored as binary data (BLOB). This could be for encryption purposes, where text data is encrypted and stored as binary data, or when preparing data for network transmission where binary format is required.
Considerations
Ensure that the destination BLOB has sufficient space to hold the converted data.
Be mindful of the character set implications, especially if the source data includes characters that might not directly map to the binary format or requires specific encoding.
Check the warning parameter after execution to handle any potential issues gracefully, such as data truncation or character set conversion warnings.
DBMS_LOB.CONVERTTOBLOB is a key tool in the Oracle DBA’s toolkit, offering flexibility in managing and converting LOB data between different formats to meet various application requirements.