barcode generator in codeproject Using the Positioned DELETE Statement in Software

Draw Code 3/9 in Software Using the Positioned DELETE Statement

Using the Positioned DELETE Statement
Code 39 Full ASCII Decoder In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Code-39 Encoder In None
Using Barcode generation for Software Control to generate, create Code 3/9 image in Software applications.
The positioned DELETE statement, like the positioned UPDATE statement, requires a WHERE clause that must include the CURRENT OF option. (A regular DELETE statement, as you ll recall, does not require the WHERE clause.) A positioned DELETE statement uses the following syntax: DELETE <table name> WHERE CURRENT OF <cursor name> As you can see, you need to define a DELETE clause that identifies the table and a WHERE clause that identifies the cursor. The WHERE clause in a positioned DELETE statement works just like the WHERE clause in a positioned UPDATE statement: The row returned by the last FETCH statement is the row that is modified. In this case, the row is deleted. Now let s look at an example of a positioned DELETE statement. The following SQL statements declare the CD_4 cursor, open the cursor, return a row from the cursor, delete that row, and close the cursor:
Recognize ANSI/AIM Code 39 In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
Code 3/9 Encoder In C#
Using Barcode printer for VS .NET Control to generate, create Code 39 Extended image in .NET framework applications.
USS Code 39 Creation In VS .NET
Using Barcode creation for ASP.NET Control to generate, create Code 39 image in ASP.NET applications.
Draw Code 39 Full ASCII In .NET Framework
Using Barcode generator for .NET Control to generate, create Code39 image in VS .NET applications.
Paint Code-39 In Visual Basic .NET
Using Barcode printer for .NET Control to generate, create Code 3 of 9 image in .NET applications.
Encode Barcode In None
Using Barcode encoder for Software Control to generate, create bar code image in Software applications.
Using SQL Cursors
GTIN - 12 Generation In None
Using Barcode creator for Software Control to generate, create UPC-A image in Software applications.
Painting Bar Code In None
Using Barcode generator for Software Control to generate, create barcode image in Software applications.
GS1-128 Generator In None
Using Barcode drawer for Software Control to generate, create EAN / UCC - 13 image in Software applications.
Generating Code 39 Full ASCII In None
Using Barcode generator for Software Control to generate, create Code-39 image in Software applications.
You should be familiar with most of these statements. The only new one is the positioned DELETE statement. This statement deletes the row returned by the FETCH statement, which is the Famous Blue Raincoat row. Once the row is deleted, the cursor is closed using a CLOSE statement. As stated previously, it is always a good idea to explicitly close cursors when they are no longer needed.
Leitcode Encoder In None
Using Barcode encoder for Software Control to generate, create Leitcode image in Software applications.
Data Matrix 2d Barcode Reader In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
Try This 15-1
Code-39 Creation In Objective-C
Using Barcode drawer for iPhone Control to generate, create Code-39 image in iPhone applications.
Create ECC200 In Java
Using Barcode generator for Eclipse BIRT Control to generate, create Data Matrix 2d barcode image in BIRT reports applications.
Working with SQL Cursors
Code 39 Decoder In VB.NET
Using Barcode reader for .NET framework Control to read, scan read, scan image in Visual Studio .NET applications.
Matrix 2D Barcode Drawer In VB.NET
Using Barcode generation for .NET Control to generate, create Matrix Barcode image in .NET applications.
In this chapter, we looked at how to declare cursors, open those cursors, retrieve data from them, and then close them. In addition, we reviewed positioned UPDATE and DELETE statements. However, as I said earlier, cursors are used primarily in embedded SQL, which makes it difficult to fully test cursor functionality if you re limited to directly invoking SQL statements (as we are in this Try This exercise). Ideally, it would be best to embed the cursor-related SQL statements in a host language, but that is beyond the scope of this book. What complicates this issue even further is the fact that different SQL implementations support the use of cursors in an interactive environment in different ways, which can make it difficult to directly invoke cursor-related statements. Still, you should be able to execute most cursor-related statements interactively, but know that cursors are designed for use in embedded SQL and SQL client modules, so you might have to modify the statements a great deal in order to execute them. You can download the Try_This_15.txt file, which contains the SQL statements used in this exercise.
Printing Bar Code In Java
Using Barcode drawer for Android Control to generate, create bar code image in Android applications.
Printing UPCA In Java
Using Barcode encoder for Android Control to generate, create Universal Product Code version A image in Android applications.
Ideally, it would be good to walk you through each step of declaring and opening a cursor, retrieving data, and closing a cursor, but because of the nature of direct invocation, we will use fewer steps and larger blocks of statements.
Step by Step
1. Open the client application for your RDBMS and connect to the INVENTORY database. 2. The first cursor that you ll declare and access is a basic read-only cursor that retrieves data
from the COMPACT_DISCS table. The first thing you ll notice in the set of statements
SQL: A Beginner s Guide
you ll be creating is that you ll declare a variable named v_CD_NAME. You ll need to create this variable in order to fully test the FETCH statement. Keep in mind that, depending on the situation, the host language, and the product, you may or may not use this method for defining your variable. Also notice that the variable name in the FETCH statement is not preceded by a colon. This is because you ll be using direct invocation to execute these statements and, for most implementations, the name of the variable in the FETCH statement will have to be the same as the name you declared at the beginning of this set of statements. As with any SQL statement, you will find that the exact language you use to create statements varies from one product to the next. In addition, the fact that you re invoking the statements directly, rather than embedding the statements, can lead to other variations between SQL and the implementation (such as not using a colon in the variable name). For example, if you execute these statements in SQL Server, you ll have to precede your variable names with the at (@) character. Oracle deviates from the standard even more. In Oracle, you declare the cursor and variable in one block of statements. In addition, the CURSOR keyword precedes the name of the cursor, and you must use the IS keyword, rather than FOR. You must also enclose the OPEN, FETCH, and CLOSE statements in a BEGIN...END block. You will also find that not all SQL options are supported in all SQL implementations, and many products include additional features not defined in the SQL standard. Be sure to check your product s documentation before trying to declare and access any cursors. Now let s create the cursor-related statements. Enter and execute the following SQL statements:
In these statements, you first declared a variable named v_CD_NAME. Next, you declared a cursor named CD_cursor_1. The cursor definition contained a SELECT statement that was qualified with an ORDER BY clause. Because you included the ORDER BY clause, your cursor was read-only. After you declared the cursor, you opened it, fetched a row from the cursor s query results, and then closed the cursor. The FETCH statement returned the value After the Rain: The Soft Sounds of Erik Satie, which could have then been used in some other operation, had you embedded these statements. After you executed the statements, you should have received a message saying that the statements were executed successfully.
Copyright © . All rights reserved.