barcode generator project source code in vb.net The OPEN CURSOR Statement in Software

Encoder PDF 417 in Software The OPEN CURSOR Statement

The OPEN CURSOR Statement
Scan PDF417 In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Painting PDF417 In None
Using Barcode creator for Software Control to generate, create PDF-417 2d barcode image in Software applications.
The cursor must be opened before it can be used. In this example, the RDBMS may not have to retrieve any rows when you open the cursor, but for ef ciency it might decide to retrieve some number of rows and place them in a buffer for you. A buffer is merely an area of computer memory used to temporarily hold data. It is far more ef cient to use a buffer to hold some number of prefetched rows than it is going to
Scanning PDF-417 2d Barcode In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
PDF-417 2d Barcode Printer In C#.NET
Using Barcode maker for VS .NET Control to generate, create PDF417 image in .NET framework applications.
SQL Demysti ed
Generating PDF 417 In .NET
Using Barcode drawer for ASP.NET Control to generate, create PDF-417 2d barcode image in ASP.NET applications.
Draw PDF-417 2d Barcode In .NET Framework
Using Barcode creator for Visual Studio .NET Control to generate, create PDF 417 image in Visual Studio .NET applications.
the database les for every single row because computers can access memory so much faster than les in the le system. In some cases, however, the RDBMS must fetch all the rows matching a query and sort them before the rst row may be returned to the application program. You may have guessed that these are queries containing an ORDER BY to sequence the returned rows for us. If there is no index on the column(s) used for sequencing, then the RDBMS must nd and sort all of them before it knows which one is the correct one to return as the rst row (the one that sorts the lowest in the requested sequence). Although a lot goes on when a cursor is opened, the statement itself is quite simple. Here is the OPEN CURSOR statement for our example:
PDF417 Creator In VB.NET
Using Barcode creator for VS .NET Control to generate, create PDF 417 image in Visual Studio .NET applications.
Generate UPC - 13 In None
Using Barcode drawer for Software Control to generate, create EAN / UCC - 13 image in Software applications.
OPEN overdue_rentals;
Bar Code Drawer In None
Using Barcode generator for Software Control to generate, create bar code image in Software applications.
Draw Data Matrix 2d Barcode In None
Using Barcode maker for Software Control to generate, create Data Matrix 2d barcode image in Software applications.
The FETCH Statement
Code 128 Code Set C Creation In None
Using Barcode printer for Software Control to generate, create Code 128 Code Set A image in Software applications.
Code 3 Of 9 Drawer In None
Using Barcode generator for Software Control to generate, create Code 39 Extended image in Software applications.
Each time your program requires a new row from the result set, simply issue a FETCH command against the cursor. This is very much like reading the next record from a le in an older at le system. Remember that the cursor is merely a pointer into the result set. Every time a fetch is issued, the cursor is advanced one row, and the row currently pointed to is returned to the calling program (that is, the program that issued the FETCH). If there are no more rows in the result set (that is, if the cursor has been advanced past the last row in the result set), a code is returned to the calling program to indicate this. Another detail handled by the fetch is mapping the columns returned to programming language variables (called host language variables, or just host variables). This is done with the INTO clause, and naturally the syntax of the variable names will vary from one programming language to another. The general form of the FETCH statement is
Identcode Drawer In None
Using Barcode creation for Software Control to generate, create Identcode image in Software applications.
Encoding EAN / UCC - 14 In None
Using Barcode encoder for Excel Control to generate, create UCC.EAN - 128 image in Excel applications.
FETCH cursor_name [INTO variable_list];
Encoding Matrix Barcode In C#.NET
Using Barcode encoder for .NET framework Control to generate, create Matrix Barcode image in .NET applications.
Code 128C Reader In VB.NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in Visual Studio .NET applications.
Notice that the FETCH statement refers only to the cursor name and the host variables. The cursor declaration ties the cursor to the table(s) and column(s) being referenced. In most SQL implementations, host variables must be declared before they can be referenced in a FETCH statement. The syntax and rules for declaring host variables vary across SQL implementations, so you should consult your vendor s documentation for details. Here is an example that will run in most SQL implementations (the INTO clause has been intentionally left out). However, Oracle requires the INTO clause along with some other statements that start and end a PL/SQL statement block, so this example won t work in Oracle without some modi cations:
Code39 Generator In Objective-C
Using Barcode creator for iPhone Control to generate, create USS Code 39 image in iPhone applications.
Making Barcode In Visual C#.NET
Using Barcode generator for Visual Studio .NET Control to generate, create barcode image in .NET framework applications.
FETCH overdue_rentals;
EAN128 Maker In Objective-C
Using Barcode creator for iPhone Control to generate, create EAN / UCC - 13 image in iPhone applications.
USS Code 128 Printer In None
Using Barcode encoder for Online Control to generate, create Code 128C image in Online applications.
Integrating SQL into Applications
Cursor UPDATE and DELETE Statements
SQL provides a convenient way to update data selected with a cursor or to delete rows from tables referenced by a cursor fetch. Keep in mind that no SQL statement can update or delete data in more than one table, so a cursor that contains a join has some update and delete restrictions. And as noted earlier, many SQL implementations require the FOR UPDATE clause for cursors that are to be used for updates and/or deletes. A special form of UPDATE and DELETE statement is used when a cursor is involved. It contains the WHERE CURRENT OF clause that names the cursor. The row that is updated or deleted is the last one fetched by the named cursor. If no row was successfully fetched from the cursor, any statement containing WHERE CURRENT OF will fail. Here is the general syntax of the cursor UPDATE statement, followed by Oracle and Microsoft SQL Server examples:
UPDATE table_name SET column_and_value_list WHERE CURRENT OF cursor_name; UPDATE MOVIE_RENTAL SET DUE_DATE = CURRENT_DATE WHERE CURRENT OF overdue_rentals; UPDATE MOVIE_RENTAL SET DUE_DATE = getdate() WHERE CURRENT OF overdue_rentals;
Here is the general syntax of the cursor DELETE statement, followed by an example:
DELETE FROM table_name WHERE CURRENT OF cursor_name; DELETE FROM MOVIE_RENTAL WHERE CURRENT OF overdue_rentals;
Copyright © OnBarcode.com . All rights reserved.