int sqlite3_blob_open( sqlite3*, const char *zDb, const char *zTable, const char *zColumn, sqlite3_int64 iRow, int flags, sqlite3_blob **ppBlob );
This interfaces opens a handle to the BLOB located in row iRow, column zColumn, table zTable in database zDb; in other words, the same BLOB that would be selected by:
SELECT zColumn FROM zDb.zTable WHERE rowid = iRow;
Parameter zDb is not the filename that contains the database, but rather the symbolic name of the database. For attached databases, this is the name that appears after the AS keyword in the ATTACH statement. For the main database file, the database name is "main". For TEMP tables, the database name is "temp".
If the flags parameter is non-zero, then the BLOB is opened for read and write access. If the flags parameter is zero, the BLOB is opened for read-only access.
On success, SQLITE_OK is returned and the new BLOB handle is stored in *ppBlob. Otherwise an error code is returned and, unless the error code is SQLITE_MISUSE, *ppBlob is set to NULL. This means that, provided the API is not misused, it is always safe to call sqlite3_blob_close() on *ppBlob after this function it returns.
This function fails with SQLITE_ERROR if any of the following are true:
If the row that a BLOB handle points to is modified by an UPDATE, DELETE, or by ON CONFLICT side-effects then the BLOB handle is marked as "expired". This is true if any column of the row is changed, even a column other than the one the BLOB handle is open on. Calls to sqlite3_blob_read() and sqlite3_blob_write() for an expired BLOB handle fail with a return code of SQLITE_ABORT. Changes written into a BLOB prior to the BLOB expiring are not rolled back by the expiration of the BLOB. Such changes will eventually commit if the transaction continues to completion.
The sqlite3_bind_zeroblob() and sqlite3_result_zeroblob() interfaces and the built-in zeroblob SQL function may be used to create a zero-filled blob to read or write using the incremental-blob interface.