qr barcode generator vb.net Dynamic SQL Concepts in Software

Encoder QR-Code in Software Dynamic SQL Concepts

Dynamic SQL Concepts
Scanning Quick Response Code In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Encoding QR In None
Using Barcode generator for Software Control to generate, create QR Code ISO/IEC18004 image in Software applications.
The central concept of dynamic SQL is simple: don t hard-code an embedded SQL statement into the program s source code. Instead, let the program build the text of a SQL statement in one of its data areas at runtime. The program then passes the statement text to the DBMS for execution on the fly. Although the details get quite complex, all of dynamic SQL is built on this simple concept, and it s a good idea to keep it in mind. To understand dynamic SQL and how it compares with static SQL, it s useful to consider once again the process the DBMS goes through to execute a SQL statement, originally shown in Figure 17-1 and repeated here in Figure 18-1. Recall from 17 that a static SQL statement goes through the first four steps of the process at compile-time. The BIND utility (or the equivalent part of the DBMS runtime system) analyzes the SQL statement, determines the best way to carry it out, and stores the application plan for the statement in the database as part of the program development process. When the static SQL statement is executed at runtime, the DBMS simply executes the stored application plan. In dynamic SQL, the situation is quite different. The SQL statement to be executed isn t known until runtime, so the DBMS cannot prepare for the statement in advance. When the program is actually executed, the DBMS receives the text of the statement to be dynamically executed (called the statement string) and goes through all five of the steps shown in Figure 18-1 at runtime.
Recognizing QR Code 2d Barcode In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
QR Code 2d Barcode Creator In Visual C#
Using Barcode creation for .NET Control to generate, create QR Code 2d barcode image in Visual Studio .NET applications.
SQL statement SELECT A, B, C FROM X, Y WHERE A < 5000 AND C = ABC Parse statement Compile-time
Create QR-Code In VS .NET
Using Barcode creator for ASP.NET Control to generate, create QR image in ASP.NET applications.
Drawing QR In .NET
Using Barcode printer for .NET framework Control to generate, create Quick Response Code image in VS .NET applications.
Static SQL
QR Encoder In VB.NET
Using Barcode drawer for VS .NET Control to generate, create QR Code 2d barcode image in VS .NET applications.
Generating EAN 13 In None
Using Barcode generation for Software Control to generate, create EAN-13 Supplement 5 image in Software applications.
Dynamic SQL
Paint Barcode In None
Using Barcode printer for Software Control to generate, create barcode image in Software applications.
UPC-A Supplement 5 Creation In None
Using Barcode creator for Software Control to generate, create UCC - 12 image in Software applications.
Precompiler
Encode Barcode In None
Using Barcode generator for Software Control to generate, create bar code image in Software applications.
Encode Code 128 Code Set B In None
Using Barcode encoder for Software Control to generate, create Code 128 image in Software applications.
Runtime
Make USPS Confirm Service Barcode In None
Using Barcode generator for Software Control to generate, create Planet image in Software applications.
Creating USS Code 39 In Objective-C
Using Barcode generation for iPad Control to generate, create Code 39 Full ASCII image in iPad applications.
Validate statement
Barcode Drawer In .NET Framework
Using Barcode generation for .NET Control to generate, create bar code image in VS .NET applications.
EAN13 Scanner In VB.NET
Using Barcode scanner for .NET framework Control to read, scan read, scan image in .NET framework applications.
PREPARE statement
USS-128 Generator In Objective-C
Using Barcode printer for iPhone Control to generate, create UCC - 12 image in iPhone applications.
Generating EAN13 In C#
Using Barcode encoder for VS .NET Control to generate, create EAN13 image in VS .NET applications.
PART V
Scanning Data Matrix 2d Barcode In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
Encode EAN13 In Java
Using Barcode drawer for BIRT reports Control to generate, create GTIN - 13 image in Eclipse BIRT applications.
Optimize statement
BIND utility
Generate application plan Plan Binary form of SQL statement
EXECUTE IMMEDIATE statement
Runtime
Execution
EXECUTE statement
Execute application plan
FIGURE 18-1
How the DBMS processes a SQL statement
Part V:
Programming with SQL
As you might expect, dynamic SQL is less efficient than static SQL. For this reason, static SQL is used whenever possible, and many application programmers never need to learn about dynamic SQL. However, dynamic SQL has grown in importance as more and more database access moved to a client/server, front-end/back-end architecture. Database access from within personal computer applications such as spreadsheets and word processors has grown dramatically, and an entire set of PC-based front-end data entry and data access tools has emerged. All of these applications require the features of dynamic SQL. The emergence of Internet-based three-tier architectures with applications logic executing on one (mid tier) system (often composed of one or more application servers) and the database logic executing on another (back-end) system has added new importance to capabilities that have grown out of dynamic SQL. In most of these three-tier environments, the applications logic running in the middle tier is quite dynamic. It must be changed frequently to respond to new business conditions and to implement new business rules. This frequently-changing environment is at odds with the very tight coupling of applications programs and database contents implied by static SQL. As a result, most threetier architectures use a callable SQL API (described in 19) to link the middle tier to back-end databases. These APIs explicitly borrow the key concepts of dynamic SQL (for example, separate PREPARE and EXECUTE steps and the EXECUTE IMMEDIATE capability) to provide their database access. A solid understanding of dynamic SQL concepts is thus important to help a programmer understand what s going on behind the scenes of the SQL API. In performance-sensitive applications, this understanding can make all the difference between an application design that provides good performance and response times and one that does not.
Dynamic Statement Execution (EXECUTE IMMEDIATE)
The simplest form of dynamic SQL is provided by the EXECUTE IMMEDIATE statement, shown in Figure 18-2. This statement passes the text of a dynamic SQL statement to the DBMS and asks the DBMS to execute the dynamic statement immediately. To use this statement, your program goes through the following steps: 1. The program constructs a SQL statement as a string of text in one of its data areas, storing it in memory as a named variable. (Recall that program language variables used to pass information to or from the DBMS are known as host variables.) The statement can be almost any SQL statement that does not retrieve data. 2. The program passes the SQL statement to the DBMS with the EXECUTE IMMEDIATE statement. 3. The DBMS executes the statement and sets the SQLCODE/SQLSTATE values to indicate the completion status, exactly as if the statement had been hard-coded using static SQL.
Copyright © OnBarcode.com . All rights reserved.