Read a few megabytes from a BLOB in Oracle

I wish to extract a sub-BLOB (a few MBs) from a BLOB in Oracle.

The question "read first 1kb of a blob from oracle" doesn't help me, since I need to get more 开发者_StackOverflow中文版bytes than DBMS_LOB.SUBSTR can give me (it returns RAW, which supports only a few thousand bytes).

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Use DBMS_LOB.READ(lob_loc, amount, offset, buffer)