Microsoft SQL Server offers various methods for importing and working with text files. One of the most versatile techniques is through the use of the OpenDataSource command. OpenDataSource allows ad hoc access to any OLE DB accessible file, providing flexibility and convenience.
Unlike other methods such as bulk insert, DTS, or SSIS, OpenDataSource allows you to access the data without fully importing it into the server as a table. This can be particularly useful when dealing with text files where the number of columns is not equal in each row or when you need temporary access to the information immediately.
The basic structure of the OpenDataSource command for reading a text file is as follows:
SELECT * FROM OpenDataSource('Microsoft.Jet.OLEDB.4.0', 'Data Source = C:\; Extended Properties = "Text;HDR=NO;"')...test1#txt
In this example, the OpenDataSource statement is treated as the server used in a select statement, with the actual file to be read listed as the table. The data source option specifies the directory from which SQL Server should read, and the Extended Properties must include the option Text. Optionally, you can include the HDR=NO option to instruct SQL Server not to use the first row as the column headers.
For greater control over the file format, you can use a schema.ini file located in the same directory as the text file being read. The schema.ini file allows you to define the exact format of the file, including delimiters, data types, and column names for every column.
Here is an example of a schema.ini entry:
[test1.txt]
Format=TABDelimited
ColNameHeader=False
Col1=num1 text
Col2=num2 text
Col3=num3 text
Each entry in the schema.ini file must begin by specifying the filename in brackets [ ]. You can then specify the format using the Format option and indicate whether the first row has column names with the ColNameHeader option. The column information is optional for delimited files but required for fixed-width files.
OpenDataSource has several advantages over bulk insert. It can handle imperfectly formatted files by reading missing columns as nulls instead of causing errors or improperly combining lines of data. Additionally, it allows insert statements against the text file, making it possible to append to the file dynamically. However, it does not support update or delete operations.
Before using OpenDataSource, ensure that the security settings are properly configured. By default, Ad Hoc Distributed queries are disabled in SQL Server. To enable them, an administrator must execute the following commands:
EXEC sp_configure 'show advanced option', '1';
RECONFIGURE;
EXEC sp_configure 'Ad Hoc Distributed Queries', '1';
RECONFIGURE;
With its ability to handle files that bulk insert cannot, work with ad hoc queries immediately, and append to text files, OpenDataSource is a powerful tool for certain instances.
For more information, you can refer to the following resources: