Excel via Linked Servers


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Recently, I had replied to post on the #sqlhelp Twitter hashtag regarding configuring a Linked Server to an Excel file using the GUI in Management Studio. This is very much possible. I use a linked server to pull data from .xls file on a 64-bit SQL Server instance for an application that I maintain.

Using the 64-bit ACE provider, you can now do this. The data source which is masked in the above picture is the location of the Excel file with the full file path.

Once you have this configured, you can access the Linked Server catalogs by expanding the Linked Server in Object Explorer. Each table listed in the catalog is actually an Excel sheet.

This is fairly simple task but since this isn’t an explicit example out there for this, I thought I would do a quick post on the same.

Addedum: April 4th, 2010. After my colleague, Evan pointed out the server side support policy for ACE.

Disclaimer: The ACE redistributable link does mention the following:

The Access Database Engine 2010 Redistributable is not intended:

  • As a replacement for the Jet OLEDB Provider in server-side applications.
  • To be used within a service program or web application that relies on a Windows service.
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What does cntr_type mean?


Have you ever wondered if the cntr_type column value in the sys.sysperfinfo or sys.dm_os_performance_counters output has a significant meaning or not. Well since the column value is there, it obviously has a meaning. Additionally, if the raw values represented by the output of some of the counter types is considered at face value, then your performance base lining can take a severe beating.

Each cntr_type value meaning can be found from the WMI Performance Counter Type or Windows Server Performance Counter Type documentation on MSDN. 

The common counter types in SQL Server are:
PERF_COUNTER_RAWCOUNT | Decimal | 65536
Raw counter value that does not require calculations, and represents one sample.

PERF_COUNTER_LARGE_RAWCOUNT | Decimal | 65792
Same as PERF_COUNTER_RAWCOUNT, but a 64-bit representation for larger values.

PERF_COUNTER_COUNTER | Decimal | 272696320
Average number of operations completed during each second of the sample interval. NOTE: For "per-second counters", this value is cumulative. The rate value must be calculated by sampling the value at discrete time intervals. The difference between any two successive sample values is equal to the rate for the time interval used. For example, batch requests/sec is a per-second counter, it would show cumulative values.

PERF_COUNTER_BULK_COUNT | Decimal | 272696576
Average number of operations completed during each second of the sample interval. This counter type is the same as the PERF_COUNTER_COUNTER type, but it uses larger fields to accommodate larger values.

PERF_AVERAGE_BULK | Decimal | 1073874176 | Decimal | 537003264
Number of items processed, on average, during an operation. This counter type displays a ratio of the items processed (such as bytes sent) to the number of operations completed, and requires a base property with PERF_AVERAGE_BASE as the counter type.

PERF_LARGE_RAW_BASE | Decimal | 1073939712
Base value found in the calculation of PERF_RAW_FRACTION, 64 bits.

Example:
If you had the following values:
SQLServer:Plan Cache | Cache Hit Ratio | Temporary Tables & Table Variables | 381
SQLServer:Plan Cache | Cache Hit Ratio Base | Temporary Tables & Table Variables | 386
Then the Temp Table/Variable cache hit ratio percentage would be: 98.7% (approx.)

You can use the query below to get the comments for each counter type as discussed above:

select object_name,counter_name,instance_name,cntr_value,
case cntr_type 
	when 65792 then 'Absolute Meaning' 
	when 65536 then 'Absolute Meaning' 
	when 272696576 then 'Per Second counter and is Cumulative in Nature'
	when 1073874176 then 'Bulk Counter. To get correct value, this value needs to be divided by Base Counter value'
	when 537003264 then 'Bulk Counter. To get correct value, this value needs to be divided by Base Counter value' 
end as counter_comments
from sys.dm_os_performance_counters
where cntr_type not in (1073939712)

 

Documentation on MSDN:

WMI Performance Counter Types

http://msdn.microsoft.com/en-us/library/aa394569(VS.85).aspx

SQL Server 2005 BOL Topic

sys.dm_os_performance_counters (Transact-SQL) 

The broad classes of counters are as follows:

Non-computational Counter Types

http://msdn.microsoft.com/en-us/library/aa392713(VS.85).aspx

Basic Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa384813(VS.85).aspx

Counter Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa389384(VS.85).aspx

Timer Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa393909(VS.85).aspx

Precision Timer Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa392755(VS.85).aspx

Queue-length Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa392905(VS.85).aspx

Base Counter Types

http://msdn.microsoft.com/en-us/library/aa384811(VS.85).aspx

Statistical Counter Types

http://msdn.microsoft.com/en-us/library/aa393663(VS.85).aspx

Data Type Mapping for OLEDB Providers


I recently had a question on the #sqlhelp hashtag on Twitter regarding how OLE DB Providers map the data columns to SQL Server data types.

The Data Type Mappings for SQL Server for distributed queries are mentioned here. The DBType values for each data that you are retrieving from a non-SQL data source like Oracle, Excel, Access can be found out using RowSet Viewer. The Microsoft® Developer Network (MSDN®) Platform SDK contains an OLE DB RowsetViewer sample application written in Microsoft Visual C++®. This application enables you to connect to either the Microsoft OLE DB Provider for AS/400 and VSAM or the Microsoft OLE DB Provider for DB2, open a table window, type the host file name or DB2 database, return a rowset, and browse the contents.

Using Rowset Viewer you can get the DBType of each column returned from the remote data source. The function used is IColumnsRowset::GetColumnsRowset. Using this you can create the necessary schema on the SQL Server database which will act as the destination for the data received from the remote data source.

Happy DB Scheming! Smile