Data Type Mapping

An OLE DB provider exposes the data types of its data in terms of OLE DB type identifiers called DBTYPEs. There are two ways that data types are converted between OLE DB data types and native Microsoft® SQL Server™ data types:

Data Type Mapping from the OLE DB Provider to SQL Server

This mapping defines the allowed comparisons and expressions, and the valid explicit conversions involving remote data. The data type of remote_column corresponds to the mapped local data type as shown in the following table.

The type rules for remote table columns in expressions can be described by this rule: A given remote column value is legal in a Transact-SQL expression if the corresponding mapped SQL Server data type in the following table is legal in the same context. For example, consider the expression:

local_column operator remote_column

local_column is a local table column and remote_column is a remote table column. This is a valid expression if operator is a valid operator for the local column’s data type and for the data type to which the DBTYPE of remote_column maps.

Similarly, CAST(remote_column AS data_type_1) is allowed if the DBTYPE of remote_column maps to the SQL Server native data_type_2 and explicit conversion from data_type_2 to data_type_1 is allowed. For example, a column of data type DBTYPE_DATE on the provider side can be converted to a datetime column in SQL Server. However, the DBTYPE_DATE data cannot be converted directly to varchar.

The mapping to a SQL Server type is determined by the DBTYPE and the DBCOLUMNFLAGS values describing the column. This information comes from the provider through either the COLUMNS schema rowset, or through the IColumnsInfo interface. In the case of the COLUMNS schema rowset, the DATA_TYPE and COLUMN_FLAGS columns represent these values. In the case of the IColumnsInfo::GetColumnInfo interface, the wType and dwFlags members of the DBCOLUMNINFO structure represent this information.

The table shows data type mappings from the OLE DB provider to SQL Server. For a given column, given its DBTYPE and its DBCOLUMNFLAG value, the corresponding SQL Server data type can be found.


DBTYPE

DBCOLUMNFLAGS
SQL Server
data type
DBTYPE_I1   numeric(3, 0)1
DBTYPE_I2   smallint
DBTYPE_I4   int
DBTYPE_I8   numeric(19,0)
DBTYPE_UI1   tinyint
DBTYPE_UI2   numeric(5,0)
DBTYPE_UI4   numeric(10,0)
DBTYPE_UI8   numeric(19,0)
DBTYPE_R4   float
DBTYPE_R8   real
DBTYPE_NUMERIC   numeric
DBTYPE_DECIMAL   decimal
DBTYPE_CY   money
DBTYPE_BSTR DBCOLUMNFLAGS_ISLONG = true ntext
DBTYPE_BSTR DBCOLUMNFLAGS_ISFIXEDLENGTH = true nchar
DBTYPE_BSTR DBCOLUMNFLAGS_ISFIXEDLENGTH = false nvarchar
DBTYPE_IDISPATCH   Error
DBTYPE_ERROR   Error
DBTYPE_BOOL   bit
DBTYPE_VARIANT   nvarchar(4000)
DBTYPE_IUNKNOWN   Error
DBTYPE_GUID   uniqueidentifier
DBTYPE_BYTES DBCOLUMNFLAGS_ISLONG = true or Maximum column size > 8,000 bytes image
DBTYPE_BYTES DBCOLUMNFLAGS_ISROWVER = true, DBCOLUMNFLAGS_ISFIXEDLENGTH = true,
Column size = 8
timestamp
DBTYPE_BYTES DBCOLUMNFLAGS_ISFIXEDLENGTH = true binary
DBTYPE_BYTES DBCOLUMNFLAGS_ISFIXEDLENGTH = false varbinary
DBTYPE_STR DBCOLUMNFLAGS_ISFIXEDLENGTH = true char
DBTYPE_ STR DBCOLUMNFLAGS_ISFIXEDLENGTH = false varchar
DBTYPE_STR DBCOLUMNFLAGS_ISLONG = true or Maximum column size > 4,000 characters text
DBTYPE_WSTR DBCOLUMNFLAGS_ISFIXED nchar
DBTYPE_WSTR DBCOLUMNFLAGS_ISFIXEDLENGTH = false nvarchar
DBTYPE_WSTR DBCOLUMNFLAGS_ISLONG = true or Maximum column size > 4,000 characters ntext
DBTYPE_UDT   Error
DBTYPE_DATE   datetime
DBTYPE_DBDATE   Error
DBTYPE_DBTIME   Error
DBTYPE_DBTIMESTAMP   datetime
DBTYPE_ARRAY   Error
DBTYPE_BYREF   Ignored
DBTYPE_VECTOR   Error
DBTYPE_RESERVED   Error
1 numeric(p,s) indicates SQL Server data type numeric with precision p and scale s.


Note If the data must be converted to a native data type different from the shown default, then an explicit conversion (using either the CAST or CONVERT function) is required. For more information, see CAST and CONVERT.


Data Type Mapping from SQL Server to the OLE DB Provider

Native Microsoft SQL Server data types map to OLE/DB types using the same table name. A mapping from a SQL Server type S1 to a given OLE/DB type T is allowed if either of these exist:

  


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