Most database system do a specific job. For example, a simple system might immediate the customer for an worker wide range, then upgrade series in the EMP and DEPT platforms. In this situation, you know the cosmetics of the UPDATE declaration at precompile time. That is, you know which platforms might be modified, the restrictions described for each desk and line, which content might be modified, and the datatype of each line.
However, some applications must agree to (or build) and procedure a number of SQL statements at run time. For example, a general-purpose review author must develop different SELECT statement for the various reviews it produces. In this situation, the statement's cosmetics is unidentified until run time. Such statement can, and probably will, change from performance to performance. They are appropriately known as dynamic SQL statement.
Unlike fixed SQL statement, dynamic SQL statement are not a part of your resource system. Instead, they are held in personality post feedback to or designed by the system at run time. They can be joined interactively or study from information.
Advantages and Drawbacks of Powerful SQL
Host applications that agree to and procedure dynamically described SQL statement are handier than simply included SQL applications. Powerful SQL statement can be designed interactively with feedback from customers having little or no understanding of SQL.
For example, your system might simply immediate customers for a search situation to be used in the WHERE stipulation of a SELECT, UPDATE, or DELETE declaration. A more technical system might allow customers to choose from choices record SQL functions, table and view names, column names, and so on. Thus, dynamic SQL allows you to create extremely versatile applications.
However, some dynamic concerns require complicated development, the use of special information components, and more playback handling. While you might not find the additional handling time, you might find the development difficult unless you completely understand dynamic SQL ideas and methods.
When to Use Powerful SQL
In exercise, rule of SQL will come across nearly all your development needs. Use dynamic SQL only if you need its open-ended versatility. Its use is recommended when one of the following items is unidentified at precompile time:
Written text of the SQL declaration (commands, conditions, and so on)
The range of wide range variables
The datatypes of wide range variables
Sources to databases things such as content, indices, series, platforms, usernames, and views
Requirements for Powerful SQL Statements
To signify an energetic SQL declaration, a personality sequence must contain the writing of a real SQL declaration, but not contain the EXEC SQL stipulation, or the declaration terminator, or any of the following included SQL commands:
In most cases, the personality sequence can contain phony wide range factors. They hold locations in the SQL declaration for actual wide range factors. Because dummy host variables are just placeholders, you do not declare them and can name them anything you like.
How Powerful SQL Claims are Processed
Typically, a program encourages the consumer for the writing of an SQL declaration and of the variety factors used in the statement. Oracle then parses the MySQL declaration to make sure it satisfies format guidelines.
Next, Oracle holds the variety factors to the SQL declaration. That is, Oracle gets the details of the variety factors so that it can study or create their principles.
Then Oracle carries out the SQL declaration. That is, Oracle does what the SQL declaration asked for, such as removing series from a desk.
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