PL/SQL DBMS_LOB.COPY

The DBMS_LOB.COPY procedure in Oracle Database is a part of the DBMS_LOB package, which provides a collection of routines to manipulate LOBs (Large Objects) such as BLOBs (Binary Large Objects), CLOBs (Character Large Objects), NCLOBs (National Character Large Objects), and BFILEs (Binary Files). The DBMS_LOB.COPY procedure specifically allows you to copy a portion or the entirety of a source LOB into a destination LOB.

Syntax

The basic syntax of the DBMS_LOB.COPY procedure is as follows:

DBMS_LOB.COPY (
   dest_lob    IN OUT NOCOPY BLOB,
   src_lob     IN BLOB,
   amount      IN INTEGER,
   dest_offset IN INTEGER,
   src_offset  IN INTEGER);

dest_lob: The LOB locator to which the data is copied. It must be a locator that is initialized to a non-NULL value.
src_lob: The LOB locator from which the data is copied. It can be a BLOB, CLOB, NCLOB, or BFILE.
amount: The number of bytes (for BLOBs) or characters (for CLOBs/NCLOBs) to be copied.
dest_offset: The offset in the destination LOB at which to start the copy (the first position is 1).
src_offset: The offset in the source LOB from which to start copying (the first position is 1).

Important Notes

The dest_lob and src_lob must already be initialized; otherwise, an error will be thrown.
If the amount specified extends beyond the end of the source LOB, only the data up to the end of the source LOB will be copied.
The procedure modifies the destination LOB in place; it does not return a new LOB.
For BLOBs and BFILEs, the amount is specified in bytes, while for CLOBs and NCLOBs, it is specified in characters.
This procedure can also be used to perform operations within the same LOB (for example, copying a portion of a LOB to another position within the same LOB).

Example

Here’s an example that demonstrates how to use DBMS_LOB.COPY to copy data from one BLOB to another:

DECLARE
  src_blob BLOB;
  dest_blob BLOB;
BEGIN
  -- Assuming src_blob and dest_blob are already initialized and filled with data.
  -- Copy 100 bytes from src_blob to dest_blob starting from the first byte
  DBMS_LOB.COPY(dest_blob, src_blob, 100, 1, 1);
  -- Do further operations such as saving the dest_blob to a table.
END;

Best Practices

Ensure that LOB locators are initialized properly before passing them to DBMS_LOB.COPY.
Be mindful of the amount, dest_offset, and src_offset parameters to avoid unintentional data loss or corruption.
Remember to commit the transaction if the operation modifies persistent LOBs stored in the database to make the changes permanent.
DBMS_LOB.COPY is a powerful tool for LOB manipulation, allowing for efficient data copying and management within Oracle databases.