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Data Type Mapping with Distributed Queries

An OLE DB provider exposes the data types of its data according to OLE DB type identifiers called DBTYPEs. Data types are converted between OLE DB data types and SQL Server system data types by mapping data:

  • From OLE DB data types to SQL Server system data types. This conversion occurs when SQL Server reads data from the OLE DB data source, either in SELECT statements or in the reading side of UPDATE, INSERT, or DELETE statements.

  • From SQL Server system data types to OLE DB data types. This conversion occurs when SQL Server writes data, mostly in INSERT or UPDATE statements, into the OLE DB data source in which the modified table is a remote table.

Data type mapping from the OLE DB provider to SQL Server defines the allowed comparisons and expressions, and the valid explicit conversions that involve remote data. The mapping is shown in the table that follows.

The type validity for remote table columns in expressions can be summarized by the following rule: A remote column value is valid in a Transact-SQL expression if the corresponding mapped SQL Server data type in the Data Type Mapping table is valid in the same context.

For example, consider the expression: local_column OPERATOR remote_column. In this expression, local_column is a local table column and remote_column is a remote table column. The expression is valid if OPERATOR is a valid operator for the data type of the local column 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 system data type 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 following table shows the data type mapping table. By using the DBTYPE indicator and its DBCOLUMNFLAGS value of a column, you can find the corresponding SQL Server data type.

DBTYPE

DBCOLUMNFLAGS

SQL Server data type

DBTYPE_I1

numeric(3, 0)1

DBTYPE_I2

smallint

DBTYPE_I4

int

DBTYPE_I8

bigint

DBTYPE_UI1

tinyint

DBTYPE_UI1

numeric(5,0)

DBTYPE_UI1

numeric(10,0)

DBTYPE_UI1

numeric(20,0)

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_ISLONG = true and column size is unlimited length.

varbinary(max)

DBTYPE_BYTES

DBCOLUMNFLAGS_ISROWVER = true, DBCOLUMNFLAGS_ISFIXEDLENGTH = true, and 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 > 8,000 characters.

text

DBTYPE_STR

DBCOLUMNFLAGS_ISLONG = true and column size is unlimited length.

varchar(max)

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_WSTR

DBCOLUMNFLAGS_ISLONG = true and column size is unlimited length.

nvarchar(max)

DBTYPE_UDT

Equivalent SQL Server user-defined type, if one is registered.

DBTYPE_DATE

date, datetime, datetime2, datetimeoffset

DBTYPE_DBDATE

date, datetime, datetime2, datetimeoffset (Compatibility level is less than 9.0.)

DBTYPE_DBTIME

time, datetime, datetime2, datetimeoffset

DBTYPE_DBTIME_EX

time, datetime2, datetimeoffset

DBTYPE_DBTIMESTAMP

time, date, datetime2, datetimeoffset, datetime

DBTYPE_DBTIMESTAMP

time, date, datetime2, datetimeoffset

DBTYPE_DBTIMESTAMP

time, date, datetime2, datetimeoffset

DBTYPE_ARRAY

Error

DBTYPE_BYREF

Ignored

DBTYPE_VECTOR

Error

DBTYPE_RESERVED

Error

DBTYPE_XML

xml (Allowed only in pass-through queries.)

1 numeric(p,s) indicates the SQL Server data type numeric with precision p and scale s.

NoteNote

If the data must be converted to a SQL Server data type that is different from the shown default, an explicit conversion, by using either the CAST or CONVERT function, is required. For more information, see CAST and CONVERT (Transact-SQL).

The DBTYPE indicator and DBCOLUMNFLAGS value information comes from the provider through either the COLUMNS schema rowset or through the IColumnsInfo interface. For the COLUMNS schema rowset, the DATA_TYPE and COLUMN_FLAGS columns represent the DBTYPE and DBCOLUMNFLAGS values. For the IColumnsInfo::GetColumnInfo interface, the wType and dwFlags members of the DBCOLUMNINFO structure represent these values.

SQL Server system data types map to OLE DB types by using the mapping shown in the previous table. A mapping from a SQL Server type S1 to a specific OLE DB type T is allowed if either of these conditions exist:

  • The corresponding mapping can be found in the data type mapping table.

  • There is an allowed implicit conversion of the data type S1 to another SQL Server data type S2 and a mapping from S2 to T is defined in the data type mapping table.

The following table shows the date and time data type mapping for data sent from an OLE DB data source to an instance of SQL Server 2008. This conversion occurs when SQL Server 2008 reads data from the OLE DB data source, either in SELECT statements or in the reading side of UPDATE, INSERT, or DELETE statements. If a remote column is of a date, time, dateime2, or datetimeoffset data type, that type is returned if the database compatibility level is 100 or higher. If the compatibility level is lower, SQL Server 2008 makes an implicit conversion to datetime.

OLE DB Type

If the remote server is SQL Server 2008

return:

If the remote server is SQL Server 2005 or SQL Server 2000 return:

If the remote server is not SQL Server and the local SQL Server 2008 database compatibility level is 90 return:

If the remote server is not SQL Server and the local SQL Server 2008 database compatibility level is 100 return:

DBTYPE_DBTIMESTAMP without dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

datetime (remote column could be either datetime or smalldatetime)

datetime (remote column could be either datetime or smalldatetime)

datetime

datetime2(7)

DBTYPE_DBTIMESTAMP with dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

datetime2

Not applicable

Not applicable

Not applicable

DBTYPE_DBDATE

date

Not applicable

datetime

date

DBTYPE_DBTIME

time(0)

Not applicable

datetime

time(0)

DBTYPE_DBTIME2

time(n)

Not applicable

Not applicable

Not applicable

DBTYPE_DBTIMESTAMPOFFSET

datetimeoffset

Not applicable

Not applicable

Not applicable

The following table shows the date and time data type mapping of data sent from an instance of SQL Server 2008 to an OLE DB data destination. This conversion occurs when SQL Server 2008 writes data, mostly in INSERT or UPDATE statements, into the OLE DB data source in which the modified table is a remote table.

SQL Server 2008 data type

If the remote server is SQL Server 2008

bind with:

If the remote server is SQL Server 2005 or SQL Server 2000 bind with:

If the remote server is not SQL Server bind with:

datetime, smalldatetime

DBTYPE_DBTIMESTAMP without dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

DBTYPE_DBTIMESTAMP without dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

DBTYPE_DBTIMESTAMP without dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

datetime2(n)

DBTYPE_DBTIMESTAMP with dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

DBTYPE_DBTIMESTAMP without dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

DBTYPE_DBTIMESTAMP without dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

date

DBTYPE_DBDATE

DBTYPE_DBDATE

DBTYPE_DBDATE

time(0)

DBTYPE_DBTIME

DBTYPE_DBTIME

DBTYPE_DBTIME

time(n) (0 < n <= 7)

DBTYPE_DBTIMESTAMP (with pending date portion)

with dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

DBTYPE_DBTIMESTAMP without dwFlags being set as DBPARAMFLAGS_SS_ISVARIABLESCALE

DBTYPE_DBTIMESTAMP (with pending date portion)

datetimeoffset

DBTYPE_DBTIMESTAMPOFFSET

Not applicable

Not applicable

SQL Server 2008 executes queries that reference remote objects having the time, date, datetime2, or datetimoffset data types, either on the local or the remote server. The decision depends on the version or provider of the remote server and the type of reference. Reference types considered are a remote column or a constant, variable or local column.

Non-SQL Server Providers

Support is partial for time, date, and datetime2 data types when similar types exist on the remote server for non-SQL Server providers. These providers do not have a way of declaring their support for these types. 

The following table shows whether a query is executed on the remote or local server. The first columns show the data type on the local server. The second column shows the corresponding OLE DB data type that the local instance of SQL Server 2008 uses for the remote server. The last three columns show whether the query is executed on the remote or local server. Execution location depends on the version or the type of the remote server.

Local server data type

Remote server OLE DB data type that is used by the local SQL Server 2008

SQL Server 2008 or a later version of remote server

SQL Server 2005 remote server

Non-MSSQL remote server

datetime

DBTYPE_DBTIMESTAMP

Remote

Remote

Remote

smalldatetime

DBTYPE_DBTIMESTAMP

Remote

Remote

Remote

datetime2

DBTYPE_DBTIMESTAMP

Remote

Local

Remote

datetimeoffset

DBTYPE_DBTIMESTAMPOFFSET

Remote

Local

Local

date

DBTYPE_DBDATE

Remote

Local

Remote

time(>0)

DBTYPE_DBTIME2

Remote

Local

Local

time(0)

DBTYPE_DBTIME2

Remote

Local

Remote

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