Difference Between Cursor And Ref Cursor In Oracle Pl Sql Tutorial Pdf
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Stored procedures are stored inside the database. They define a programming interface for the database rather than allowing the client application to interact with database objects directly. Stored procedures are typically used for data validation or to encapsulate large, complex processing instructions that combine several SQL queries.
Oracle Database Data Cartridge Developer's Guide for information about creating aggregate functions for complex data types such as multimedia data stored using object types, opaque types, and LOBs.
A block has an optional declarative part, a required executable part, and an optional exception-handling part. A block can be either anonymous or named. If the subprogram has parameters, then their values can differ for each invocation. A subprogram is either a procedure or a function. Typically, you use a procedure to perform an action and a function to compute and return a value.
Package subprograms and standalone programs are stored subprograms. A stored subprogram is compiled and stored in the database, where many applications can invoke it. The 3GL subprogram runs in a separate address space from that of the database. For information about external subprograms, see Chapter 18, "Developing Applications with Multiple Programming Languages. Overloaded subprograms have the same name but their formal parameters differ in either name, number, order, or data type family.
Unlike a stored procedure, you can enable and disable a trigger, but you cannot explicitly invoke it. While a trigger is enabled, the database automatically invokes it—that is, the trigger fires—whenever its triggering event occurs. While a trigger is disabled, it does not fire. A package is compiled and stored in the database, where many applications can share its contents. A package always has a specification , which declares the public items that can be referenced from outside the package.
If the public items include cursors or subprograms, then the package must also have a body. The body must define queries for public cursors and code for public subprograms.
The body can also declare and define private items that cannot be referenced from outside the package, but are necessary for the internal workings of the package. Finally, the body can have an initialization part , whose statements initialize variables and do other one-time setup steps, and an exception-handling part.
You can change the body without changing the specification or the references to the public items; therefore, you can think of the package body as a black box. In either the package specification or package body, you can map a package subprogram to an external Java or C subprogram by using a call specification , which maps the external subprogram name, parameter types, and return type to their SQL counterparts. The AUTHID clause of the package specification determines whether the subprograms and cursors in the package run with the privileges of their definer the default or invoker, and whether their unqualified references to schema objects are resolved in the schema of the definer or invoker.
You use this clause in situations like these:. You want clients to have access to the API, but not to the helper packages. Example creates two procedures, displays their optimize levels, changes the optimize level for the session, creates a third procedure, and displays the optimize levels of all three procedures.
Only the third procedure has the new optimize level. Then the example changes the optimize level for only one procedure and displays the optimize levels of all three procedures again. If the subprogram or package that you create references schema objects, then you must have the necessary object privileges for those objects. These privileges must be granted to you explicitly, not through roles. If the privileges of the owner of a subprogram or package change, then the subprogram or package must be reauthenticated before it is run.
If a necessary object privilege for a referenced object is revoked from the owner of the subprogram or package, then the subprogram cannot run. Granting the EXECUTE privilege on a subprogram lets users run that subprogram under the security domain of the subprogram owner, so that the user need not be granted privileges to the objects that the subprogram references.
Furthermore, it allows subprograms and packages to be stored in the data dictionary in the SYSTEM tablespace , where no quota controls the amount of space available to a user who creates subprograms and packages. The DDL statements for creating standalone subprograms and packages are:. The name of a package and the names of its public objects must be unique within the package schema.
The package specification and body must have the same name. Package constructs must have unique names within the scope of the package, except for overloaded subprograms.
Using any text editor, create a text file that contains DDL statements for creating any number of subprograms and packages. This is not the size in the shared pool. For the reasons, see Section 7. Scalar data types store values that have no internal components. A scalar data type can have subtypes. A subtype is a data type that is a subset of another data type, which is its base type. A subtype has the same valid operations as its base type. A data type and its subtypes comprise a data type family.
NULL represents an unknown value. A cursor variable is like an explicit cursor, except that:. You can open a cursor variable for a query, process the result set, and then use the cursor variable for another query. A cursor variable has this flexibility because it is a pointer; that is, its value is the address of an item, not the item itself. Composite data types have internal components.
In a collection , the internal components always have the same data type, and are called elements. You can access each element of a collection variable by its unique index. In a record , the internal components can have different data types, and are called fields.
You can access each field of a record variable by its name. A cursor that you construct and manage is an explicit cursor. A cursor variable is a pointer to a cursor. That is, its value is the address of a cursor, not the cursor itself. Therefore, a cursor variable has more flexibility than an explicit cursor.
However, a cursor variable also has costs that an explicit cursor does not. You cannot pass parameters to a cursor variable, but you can pass whole queries to it. The queries can include variables. If you must change the cursor, then you must change only the stored subprogram, not every application that invokes the stored subprogram. The application connects to the server with the user name of the application user.
If you do not need to use a cursor variable, then use an implicit or explicit cursor, for both better performance and ease of programming. Avoiding a parse can significantly reduce CPU use, and the caching of explicit cursors is transparent to you; it does not affect your programming. If your program must open another cursor but doing so would exceed the init. Therefore, a cursor variable has a parsing penalty. In Example , the procedure opens, fetches from, and closes an explicit cursor and then does the same with a cursor variable.
The anonymous block calls the procedure 10 times. The TKPROF report shows that both queries were run 10 times, but the query associated with the explicit cursor was parsed only once, while the query associated with the cursor variable was parsed 10 times.
Example Parsing Penalty for Cursor Variable. Example creates a table that has more than 7, rows and fetches all of those rows twice, first with an implicit cursor fetching arrays and then with a cursor variable fetching individual rows.
The code for the implicit cursor is simpler than the code for the cursor variable, and the TKPROF report shows that it also performs better. Although you could use the cursor variable to fetch arrays, you would need much more code. Specifically, you would need code to do the following:. You might pass the data through a series of transformations, each performed by a different function.
These functions can accept and return multiple rows, can return rows as they are ready rather than all at once, and can be parallelized. Subsequently, when the same function is invoked with the same parameter values, the result is retrieved from the cache, instead of being recomputed. Because the cache is stored in a shared global area SGA , it is available to any session that runs your application. If a database object that was used to compute a cached result is updated, the cached result becomes invalid and must be recomputed.
The best candidates for result-caching are functions that are invoked frequently but depend on information that changes infrequently or never. Every SQL statement causes a context switch between the two engines. When a SQL statement runs inside a loop that uses collection elements as bind variables, the large number of context switches required can cause poor performance.
Collections include:. Bulk binding is binding an entire collection at once. Bulk binds pass the entire collection between the two engines in a single operation. Typically, bulk binding improves performance for SQL statements that affect four or more database rows.
The more rows affected by a SQL statement, the greater the performance gain from bulk binding. The actions are performed with and without bulk binds. It is useful when writing general-purpose and flexible programs like ad hoc query systems, when writing programs that must run database definition language DDL statements, or when you do not know at compile time the full text of a SQL statement or the number or data types of its input and output variables.
Successful compilation verifies that static SQL statements reference valid database objects and that the necessary privileges are in place to access those objects. For information about schema object dependency, see Section 23, "Schema Object Dependency. To alter the name of a stored standalone subprogram or package, you must drop it as instructed in Section For example:.
To drop stored standalone subprograms, use these statements:. For details, see Section You do not need privileges to invoke:. Some interactive tools allow you to create session variables, which you can use for the duration of the session.
The difference between cursor and refcursor and sys_refcursor
This does not apply to a BULK or multirow operation. Oracle is transaction oriented; that is, Oracle uses transactions to ensure data integrity. A transaction is a series of SQL data manipulation statements that does a logical unit of work. It is important not to allow one operation to succeed while the other fails. At the end of a transaction that makes database changes, Oracle makes all the changes permanent or undoes them all. If your program fails in the middle of a transaction, Oracle detects the error and rolls back the transaction, restoring the database to its former state. Example shows some queries that call SQL functions.
New Features in PL/SQL for Oracle Database 10g Release 2 () . .. xxv Differences between the CHAR and VARCHAR2 Datatypes. Declaring REF CURSOR Types and Cursor Variables. Reducing Loop Overhead for DML Statements and Queries with Bulk SQL.
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It allows declaration of constants and variables , procedures and functions, types and variables of those types, and triggers. It can handle exceptions run-time errors. Implementations from version 8 of Oracle Database onwards have included features associated with object-orientation. These keywords divide the block into a declarative part, an executable part, and an exception-handling part. The declaration section is optional and may be used to define and initialize constants and variables.
I believe that many DBAs who do development or maintenance have encountered similar problems when looking for a job: simply describe the type of cursor, the difference between a normal cursor and a REF cursor, and when to apply it correctly. This topic, I really puzzled a lot of people, in fact, they are in the specific development of the time, it is still more able to grasp the correct use of the cursor, but that is not to say, of course, this and everyone's own channel flow traffic capacity is related. Some people are not good at speaking, but they are doing well. Pull the pull away, finally nagging: do technology this road, can not say, or will do not packaging, road is not "far".
What is CURSOR in PL/SQL?
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