Oracle数据库：如何读取BLOB？

UTL_RAW.CAST_TO_RAW(UTL_RAW.CAST_TO_VARCHAR2())

SELECT b FROM foo;
-- (BLOB)

SELECT UTL_RAW.CAST_TO_RAW(UTL_RAW.CAST_TO_VARCHAR2(b))
FROM foo;
-- 1F8B080087CDC1520003F348CDC9C9D75128CF2FCA49D1E30200D7BBCDFC0E000000

CREATE GLOBAL TEMPORARY TABLE foo (
    b BLOB);
INSERT INTO foo VALUES (\'1f8b080087cdc1520003f348cdc9c9d75128cf2fca49d1e30200d7bbcdfc0e000000\');

DESC foo;
-- Name Null Type 
-- ---- ---- ---- 
-- B        BLOB 

SELECT CAST ( <blobfield> AS RAW( <maxFieldLength> ) ) FROM <table>;

SELECT DUMP ( CAST ( <blobfield> AS RAW( <maxFieldLength> ) ) ) FROM <table>;

Dim cn As New Oracle.DataAccess.Client.OracleConnection
Dim cm As New Oracle.DataAccess.Client.OracleCommand
Dim dr As Oracle.DataAccess.Client.OracleDataReader

\"Data Source=myOracle;UserID=Me;Password=secret\"

cn.ConnectionString = \"Data Source=myOracle;UserID=Me;Password=secret\"
cn.Open()

cm.Connection = cn
cm.CommandText = strCommand

cm.InitialLONGFetchSize = 4000

dr = cm.ExecuteReader

Do while dr.read()
    strMyLongString = dr(i)
Loop

dr(i)

dr.GetOracleString(i)

CTX_DOC.POLICY_FILTER