각 DB데이터 필드 타입에 따라 .NET의 DataReader를 통해 읽었을때 자료형이 달라진다.
아래 표를 참고하면 어떤 형식으로 읽혀지는지 쉽게 구분가능하다.

.NET Framework 형식	SQL Server 형식	Oracle 형식	ADO 형식	ODBC 형식
Byte	tinyint		adTinyInt adUnsignedTinyInt	SQL_TINYINT
Byte[]	binary image timestamp varbinary	BFILE BLOB LONG RAW RAW	adBinary	SQL_BINARY SQL_LONGVARBINARY SQL_VARBINARY
Int16	smallint		adSmallInt	SQL_SMALLINT
Int32	int	INTERVAL YEAR TO MONTH *	adInteger	SQL_INTEGER
Int64	bigint		adBigInt	SQL_BIGINT
UInt16			adUnsignedSmallInt
UInt32			adUnsignedInt
UInt64			adUnsignedBigInt
Decimal	decimal money numeric smallmoney	FLOAT INTEGER NUMBER UNSIGNED INTEGER	adCurrency adDecimal adNumeric	SQL_DECIMAL SQL_NUMERIC
Double	float		adDouble	SQL_DOUBLE
DateTime	datetime smalldatetime	DATE TIMESTAMP * TIMESTAMP WITH LOCAL TIME ZONE * TIMESTAMP WITH TIME ZONE *	adDate adDBDate adDBTime adDBTimeStamp adFileTime	SQL_TYPE_TIMES SQL_TYPE_TIMESTAMP
String			adBSTR adChar adWChar
String Char[]	char nchar ntext nvarchar text varchar	CHAR CLOB LONG NCHAR NCLOB NVARCHAR2 ROWID VARCHAR2		SQL_CHAR SQL_LONG_VARCHAR SQL_WCHAR SQL_WLONGVARCHAR SQL_WVARCHAR
Guid	uniqueidentifier		adGUID	SQL_GUID
Boolean	bit		adBoolean	SQL_BIT
Xml	xml
Object			adIDispatch adIUnknown adPropVariant adVariant
Object *	sql_variant
TimeSpan		INTERVAL DAY TO SECOND *
Single	real		adSingle	SQL_REAL
ExternalException			adError
DataReader를 통해 지원			adChapter
지원되지 않음		REF CURSOR	adUserDefined adVarNumeric