qr barcode generator vb.net The SQL/PSM Triggers Standard in Software

Print QR Code in Software The SQL/PSM Triggers Standard

The SQL/PSM Triggers Standard
Recognizing QR Code In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
QR-Code Generation In None
Using Barcode generation for Software Control to generate, create Quick Response Code image in Software applications.
Triggers were addressed for standardization as part of the SQL3 effort, which led to the eventual publication of the SQL:1999 ANSI/ISO standard. By that time, many commercial DBMS products had already implemented triggers, and the standard synthesized the specific capabilities that had proven useful in practice. Like the commercial products, ANSI/ISO standard triggers are defined for a single, specific table. The standard permits trigger definitions only on tables, not on views. The proprietary SQL Server, Oracle, and Informix trigger mechanisms shown in the examples throughout this chapter provide a context for examining the ANSI/ISO
Scanning QR In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
Drawing QR Code JIS X 0510 In C#
Using Barcode printer for .NET framework Control to generate, create QR Code JIS X 0510 image in .NET applications.
20:
QR Code 2d Barcode Generator In .NET Framework
Using Barcode creation for ASP.NET Control to generate, create QR image in ASP.NET applications.
QR Drawer In VS .NET
Using Barcode encoder for .NET Control to generate, create QR Code image in VS .NET applications.
Database Processing and Stored Procedural SQL
QR Code Drawer In VB.NET
Using Barcode encoder for .NET Control to generate, create QR image in VS .NET applications.
Generating Code-128 In None
Using Barcode generation for Software Control to generate, create Code 128 image in Software applications.
standard mechanism. The standard does not provide any radical departure from the capabilities already described for the various DBMS products. Here is how the standard compares with them: Naming The standard treats triggers as named objects within the database. Types The standard provides INSERT, DELETE, and UPDATE triggers; UPDATE triggers can be associated with the update of a specific column or group of columns. Timing The standard provides for triggers that operate before a database update statement or after the statement. Row-level or statement-level operation The standard provides for both statement-level triggers (executed once per database-updating statement) and rowlevel triggers (executed repeatedly for each row of the table that is modified). Aliases Access to the before and after values in a modified row or table is provided via an alias mechanism, like the table aliases used in the FROM clause. You use the CREATE TRIGGER statement, shown in Figure 20-23, to define a trigger. The statement clauses are familiar from the proprietary trigger examples throughout the earlier sections of this chapter.
Drawing GTIN - 13 In None
Using Barcode printer for Software Control to generate, create GTIN - 13 image in Software applications.
Bar Code Creator In None
Using Barcode encoder for Software Control to generate, create barcode image in Software applications.
PART VI
Creating GTIN - 128 In None
Using Barcode generator for Software Control to generate, create EAN / UCC - 14 image in Software applications.
Bar Code Generation In None
Using Barcode creation for Software Control to generate, create bar code image in Software applications.
FIGURE 20-23
USPS POSTal Numeric Encoding Technique Barcode Creation In None
Using Barcode creator for Software Control to generate, create Postnet image in Software applications.
Code 39 Generator In Java
Using Barcode encoder for Android Control to generate, create Code 39 image in Android applications.
The SQL standard CREATE TRIGGER syntax diagram
Draw Bar Code In Visual C#
Using Barcode drawer for Visual Studio .NET Control to generate, create bar code image in VS .NET applications.
Create Code-39 In Visual C#
Using Barcode drawer for .NET framework Control to generate, create Code 39 Extended image in Visual Studio .NET applications.
Part VI:
Bar Code Generator In Visual C#
Using Barcode generation for Visual Studio .NET Control to generate, create barcode image in .NET applications.
Bar Code Generator In Java
Using Barcode creator for BIRT reports Control to generate, create bar code image in BIRT reports applications.
SQL Today and Tomorrow
Encode Bar Code In Java
Using Barcode drawer for Eclipse BIRT Control to generate, create bar code image in Eclipse BIRT applications.
Scan Barcode In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
One very useful extension provided by the standard is the WHEN clause that can be specified as part of a triggered action. The WHEN clause is optional, and it operates like a WHERE clause for determining whether a triggered action will be carried out. When the DBMS executes the particular type of statement specified in the trigger definition, it evaluates the search condition specified in the WHEN clause. The form of the search condition is exactly like the search condition in a WHERE clause, and it will produce either a TRUE or FALSE result. The triggered action is carried out only if the result is TRUE. To provide security for triggers, the SQL standard establishes a new TRIGGER privilege that may be granted for specific tables to specific users. With this privilege, a user may establish a trigger on the table. The owner of a table is always allowed to establish triggers on the table.
Summary
Stored procedures and triggers are two very useful capabilities for SQL databases used in transaction-processing applications: Stored procedures allow you to predefine common database operations, and invoke them simply by calling the stored procedure, for improved efficiency and less chance of error. Extensions to the basic SQL language give stored procedures the features normally found in programming languages. These features include local variables, conditional processing, branching, and special statements for row-by-row query results processing. Stored functions are a special form of stored procedure that return a single value, or in some implementations, a single object or XML document. Triggers are procedures whose execution is automatically initiated based on attempted modifications to a table. A trigger can be fired by an INSERT, DELETE, or UPDATE statement for the table, or in some implementations, a system event. The specific SQL dialects used by the major DBMS brands to support stored procedures and triggers vary widely. There is now an international standard for stored procedures, functions, and triggers. As one of the newer standards, it has not yet had a major impact on implementation by leading DBMS vendors.
Copyright © OnBarcode.com . All rights reserved.