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ODBC Applications: Writing Good Code in .NET Integrated data matrix barcodes in .NET ODBC Applications: Writing Good Code




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ODBC Applications: Writing Good Code using barcode integrated for .net vs 2010 control to generate, create data matrix barcode image in .net vs 2010 applications. Oracle Reports Service can retrieve da ECC200 for .NET ta from the server in arrays, further improving the performance by reducing network traffic. For ODBC drivers that do not support SQLExtendedFetch, your application can enable forward-only cursors using the ODBC cursor library by calling SQLSetConnectAttr.

Using the cursor library won t improve performance, but it also won t decrease application response time when using forward-only cursors because no logging is required. For scrollable cursors, it s a different story (see Using the Cursor Library, page 141). In addition, using the cursor library when SQLExtendedFetch is not supported natively by the driver simplifies code because the application can always depend on SQLExtendedFetch being available.

The application doesn t require two algorithms (one using SQLExtendedFetch and one using SQLFetch). Determining the Number of Rows in a Result Set ODBC defines two types of cursors: Forward-only Scrollable (static, keyset-driven, dynamic, and mixed) Scrollable cursors let you go both forward and backward through a result set. However, because of limited support for server-side scrollable cursors in many database systems, ODBC drivers often emulate scrollable cursors, storing rows from a scrollable result set in a cache on the machine where the driver resides (client or application server).

Unless you are certain that the database natively supports using a scrollable result set, do not call the SQLExtendedFetch function to find out how many rows the result set contains. For drivers that emulate scrollable cursors, calling SQLExtendedFetch causes the driver to retrieve all results across the network to reach the last row. This emulated model of scrollable cursors provides flexibility for the developer but comes with a performance penalty until the client cache of rows is fully populated.

Instead of calling SQLExtendedFetch to determine the number of rows, count the rows by iterating through the result set or obtain the number of rows by submitting a Select statement with the Count function. For example:. SELECT COUNT(*) FROM employees Unfortunately, data matrix barcodes for .NET there s no easy way to tell if a database driver uses native server-side scrollable cursors or emulates this functionality. For Oracle or.

Updating Data MySQL, you know .net framework Data Matrix ECC200 the driver emulates scrollable cursors, but for other databases, it s more complicated. See Using Scrollable Cursors, page 36, for details about which common databases support server-side scrollable cursors and how database drivers emulate scrollable cursors.

. Performance Tip In general, do not write code that relies on the number of result rows from a query because drivers often must retrieve all rows in a result set to determine how many rows the query will return.. Choosing the Ri ECC200 for .NET ght Data Type When designing your database schema, it s obvious that you need to think about the impact of storage requirements on the database server. Less obvious, but just as important, you need to think about the network traffic required to move data in its native format to and from the ODBC driver.

Retrieving and sending certain data types across the network can increase or decrease network traffic.. Performance Tip For multiuser, multivolume applications, billions, or even trillions, of network packets can move between the driver and the database server over the course of a day. Choosing data types that are processed efficiently can incrementally provide a measurable gain in performance..

See Choosing t data matrix barcodes for .NET he Right Data Type, page 34, for information about which data types are processed faster than others..

Updating Data Use the guideli .net vs 2010 datamatrix 2d barcode nes in this section to manage your updates more efficiently. Using SQLSpecialColumns to Optimize Updates and Deletes Many databases have hidden columns, named pseudo-columns, that represent a unique key associated with every row in a table.

Typically, pseudo-columns in a. ODBC Applications: Writing Good Code SQL statement p Visual Studio .NET datamatrix 2d barcode rovide the fastest way to access a row because they usually point to the exact location of the physical record..

Performance Tip Use SQLSpecialColumns to identify the most optimal columns, typically pseudo-columns, to use in the Where clause for updating data.. Some applicatio Data Matrix for .NET ns, such as an application that forms a Where clause consisting of a subset of the column values retrieved in the result set, cannot be designed to take advantage of positioned updates and deletes. Some applications may formulate the Where clause by using searchable result columns or by calling SQLStatistics to find columns that may be part of a unique index.

These methods usually work but can result in fairly complex queries. For example:. rc = SQLExecDir ect (hstmt, "SELECT first_name, last_name," + "ssn, address, city, state, zip" + "FROM employees", SQL_NTS); // fetch data using complex query ...

rc = SQLExecDirect (hstmt, "UPDATE employees SET address = " + "WHERE first_name = AND last_name = " + "AND ssn = AND address = AND city = AND" + "state = AND zip = ", SQL_NTS);. Many databases Data Matrix barcode for .NET support pseudo-columns that are not explicitly defined in the table definition but are hidden columns of every table (for example, ROWID for Oracle). Because pseudo-columns are not part of the explicit table definition, they re not retrieved when SQLColumns is called.

To determine if pseudo-columns exist, your application must call SQLSpecialColumns. For example:. ...

rc = SQLSpe cialColumns (hstmt, SQL_BEST_ROWID, ...

); ...

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