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Function SEEK

RDB$BLOB_UTIL.SEEK sets the position for the next READ_DATA, it returns the new position.

MODE may be:

0

from the start

1

from current position

2

from end.

When MODE is 2, OFFSET should be zero or negative.

Input parameters
  • HANDLE type INTEGER NOT NULL

  • MODE type INTEGER NOT NULL

  • OFFSET type INTEGER NOT NULL

Return type: INTEGER NOT NULL.

Note

SEEK only works on stream blobs.Attempting to seek on a segmented blob results in error “invalid BLOB type for operation”.

Procedure CANCEL_BLOB

RDB$BLOB_UTIL.CANCEL_BLOB immediately releases a temporary BLOB, like one created with BLOB_APPEND.

If the same BLOB is used after cancel, an “invalid blob id” error will be raised.

Input parameter
  • BLOB type BLOB

Procedure CLOSE_HANDLE

RDB$BLOB_UTIL.CLOSE_HANDLE closes a BLOB handle opened with RDB$BLOB_UTIL.OPEN_BLOB.

Handles which are not explicitly closed are closed automatically when the transaction ends.

Input parameter
  • HANDLE type INTEGER NOT NULL

Examples

Create a BLOB in temporary space and return it in EXECUTE BLOCK
execute block returns (b blob)
as
begin
    -- Create a BLOB handle in the temporary space.
    b = rdb$blob_util.new_blob(false, true);

    -- Add chunks of data.
    b = blob_append(b, '12345');
    b = blob_append(b, '67');

    suspend;
end
Open a BLOB and return chunks of it with EXECUTE BLOCK
execute block returns (s varchar(10))
as
    declare b blob = '1234567';
    declare bhandle integer;
begin
    -- Open the BLOB and get a BLOB handle.
    bhandle = rdb$blob_util.open_blob(b);

    -- Get chunks of data as string and return.

    s = rdb$blob_util.read_data(bhandle, 3);
    suspend;

    s = rdb$blob_util.read_data(bhandle, 3);
    suspend;

    s = rdb$blob_util.read_data(bhandle, 3);
    suspend;

    -- Here EOF is found, so it returns NULL.
    s = rdb$blob_util.read_data(bhandle, 3);
    suspend;

    -- Close the BLOB handle.
    execute procedure rdb$blob_util.close_handle(bhandle);
end
Seek in a blob
set term !;

execute block returns (s varchar(10))
as
    declare b blob;
    declare bhandle integer;
begin
    -- Create a stream BLOB handle.
    b = rdb$blob_util.new_blob(false, true);

    -- Add data.
    b = blob_append(b, '0123456789');

    -- Open the BLOB.
    bhandle = rdb$blob_util.open_blob(b);

    -- Seek to 5 since the start.
    rdb$blob_util.seek(bhandle, 0, 5);
    s = rdb$blob_util.read_data(bhandle, 3);
    suspend;

    -- Seek to 2 since the start.
    rdb$blob_util.seek(bhandle, 0, 2);
    s = rdb$blob_util.read_data(bhandle, 3);
    suspend;

    -- Advance 2.
    rdb$blob_util.seek(bhandle, 1, 2);
    s = rdb$blob_util.read_data(bhandle, 3);
    suspend;

    -- Seek to -1 since the end.
    rdb$blob_util.seek(bhandle, 2, -1);
    s = rdb$blob_util.read_data(bhandle, 3);
    suspend;
end!

set term ;!
Check if blobs are writable
create table t(b blob);

set term !;

execute block returns (bool boolean)
as
    declare b blob;
begin
    b = blob_append(null, 'writable');
    bool = rdb$blob_util.is_writable(b);
    suspend;

    insert into t (b) values ('not writable') returning b into b;
    bool = rdb$blob_util.is_writable(b);
    suspend;
end!

set term ;!