Tài liệu Oracle PL/SQL Language Pocket Reference- P25 pdf

PROCEDURE calc_profits (company_id_in IN NUMBER, profit_type_in IN VARCHAR2 := 'NET'); If I try to use this procedure in Oracle Forms, I must include a value for both parameters, even if I use the default: calc_profits (:company.company_id, 'NET'); Suppose I now create the following local procedure (either in the form itself or in a PL/SQL library): PROCEDURE of_calc_profits (company_id_in IN NUMBER, profit_type_in IN VARCHAR2 := 'NET') IS BEGIN calc_profits (company_id_in, profit_type_in); END; I can now call this procedure using the default value of NET, since the Oracle Forms version of the procedure always passes a value to the stored procedure version: of_calc_profits (:company.company_id); (In Version 7.1 of the Oracle Server, by the way, you will be permitted to use default values in remote procedure calls.) This situation with Oracle Server Version 7 reinforces one of my suggestions regarding default parameter values: always specify a value for each of the module's parameters, even if a value is the same as the default. You will find yourself less vulnerable to problems down the line. Previous: 22.6 Construct Abstract Data Types (ADTs) Oracle PL/SQL Programming, 2nd Edition Next: 23. Managing Code in the Database 22.6 Construct Abstract Data Types (ADTs) Book Index 23. Managing Code in the Database The Oracle Library Navigation Copyright (c) 2000 O'Reilly & Associates. All rights reserved. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Previous: 22.7 Tips for Parameter Design Chapter 23 Next: 23.2 Transaction Integrity and Execute Authority 23. Managing Code in the Database Contents: Executing Stored Code Transaction Integrity and Execute Authority Module Validation and Dependency Management Remote Procedure Calls Managing Stored Objects with SQL*Plus Using SQL to Examine Stored Objects Encrypting Stored Code You will either embed PL/SQL programs in your client-side application, as happens in the Oracle Developer/2000 tools, or you will store your code in the Oracle database. The term stored procedure commonly refers to code that is stored in the database. Along with procedures, you can also store functions and packages, which can contain variables, cursors, record structures, etc. Whenever you hear the term stored procedures, you should think "stored objects." There are a number of benefits to storing an object in the database: ● The database manages dependencies between your stored objects. For example, if a stored function relies on a certain table and that table's structure is changed, the status of that function is automatically set to INVALID and recompilation takes place, again automatically, when someone tries to execute that function. ● Any session with EXECUTE authority can execute the stored object. Whether you are in an Oracle Forms application, a database trigger, or a batch process, that stored object is accessible as long as the database is accessible. The compiled code for the object is made available from the shared memory of the database instance. ● You can execute a module stored in another (remote) database. This is known as a remote procedure call, or RPC. The ability to execute code on a different database means that you do not have to distribute application code to multiple databases in order to support distributed applications. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. ● Stored modules offer transaction-level security, which goes well beyond the table- and column-level data and referential integrity offered by the database. With a stored module you can make sure that transactions involving multiple tables and different steps are always performed properly. This was actually one of the original motivations for the development of the PL/SQL language. ● Execution of a stored object shifts CPU load to the server. Rather than run your code locally in a form or report, the stored object executes on the database server. Assuming that the server is sized to handle the load, this shift could improve overall application performance. This feature could be less of a benefit, of course, if the server is already heavily burdened. Stored objects play an important role in today's client-server applications. The information in this chapter will help you make the best possible use of stored objects. 23.1 Executing Stored Code To execute a stored program unit, you must first store this program in the database. I'll explain this CREATE OR REPLACE step later in this chapter. For now, let's take a look at what happens when you run a stored PL/SQL program. 23.1.1 Executing Procedures If you are working in SQL*Plus, you can execute programs directly from the command line. Use the EXECUTE command to run procedures as follows: SQL> execute calc_totals Notice that you do not have to provide a semicolon. In fact, if you are going to use the EXECUTE command, the entire PL/SQL procedure call must fit on one physical line. As soon as you press the Enter key, the program executes. You can also save a few microseconds (but accumulated over a whole year .) by providing only the minimum number of characters for the EXECUTE command: SQL> exec calc_totals When you are executing a procedure within a PL/SQL block, you do not use the EXECUTE syntax. You simply call the procedure, passing all necessary parameters within parentheses, and then terminate the line of code with a semicolon. Here is the syntax for calling the calc_totals procedure within a PL/SQL block: BEGIN calc_totals; END; Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. You can also execute PL/SQL procedures in various "front-end" tools, such as Oracle Forms, PowerBuilder, and many 3GL languages like C and COBOL. The syntax for calling procedures (and functions) will vary from tool to tool. Within the Oracle Developer/2000 environment, you can call stored programs from within a "native," albeit outdated, version of PL/SQL (see Appendix B, Calling Stored Procedures from PL/SQL Version 1.1, for more information). From a language like C, you will actually use a precompiler called Pro*C (from Oracle) and embed calls to PL/SQL programs within a SQL execution block like this: EXEC SQL EXECUTE BEGIN calc_totals; END; END-EXEC; 23.1.2 Executing Functions The situation with functions is a little bit different. A function returns a value, so you can't just execute it directly. If you try to run a function as if it is a procedure, you will get the following error: SQL> exec total_sales (1997) begin total_sales (1997); end; * ERROR at line 1: ORA-06550: line 1, column 7: PLS-00221: 'TOTAL_SALES' is not a procedure or is undefined ORA-06550: line 1, column 7: PL/SQL: Statement ignored If you want to run a function simply to view its return value, you can execute it within a call to DBMS_OUTPUT.PUT_LINE as follows: SQL> exec DBMS_OUTPUT.PUT_LINE (total_sales (1997)) Of course, this only works if the datatype of the return value of the function matches one of the datatypes supported by DBMS_OUTPUT: number, string and date. For anything else, you will need to execute the function within an anonymous block and then convert the value as necessary for display. In the following example, I declare a PL/SQL table of strings to retrieve the value from a function that returns all the foreign key information for a table. I then use a FOR loop to display that information: /* Employs PL/SQL 2.3 syntax for PL/SQL tables. */ DECLARE TYPE strtabtype IS TABLE OF VARCHAR2(100) INDEX BY BINARY_INTEGER; Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. strtab strtabtype; BEGIN strtab := primary_keys.for_table (`emp'); IF strtab.COUNT > 0 THEN FOR tabrow IN strtab.FIRST strtab.LAST LOOP DBMS_OUTPUT.PUT_LINE (strtab.column_name); END LOOP; END IF; END; / If I have saved this block in a file called myscript.sql, I can then execute this program and verify my function's behavior as follows: SQL> @myscript NOTE: You might wonder why I placed my FOR loop inside an IF statement. Surely, if there were no rows, the strtab.FIRST method would return NULL and the loop would not execute. Yes and no. The FIRST and LAST methods do return NULL if the PL/SQL table is empty, but oddly enough, if your numeric FOR loop range evaluates to: FOR tabrow IN NULL NULL then the PL/SQL runtime engine does enter the loop and try to process the body contents immediately. Then it raises an ORA-06502 VALUE_ERROR exception. So you really want to put some conditional logic around those FOR loops if you think the range endpoints might evaluate to NULL.1 Now that you've seen how to execute programs "from the outside," let's move inside and take a look at the architecture Oracle employs to deliver that code to you for execution. 23.1.3 Memory-Based Architecture of PL/SQL Code Whenever you start up an Oracle instance, a chunk (usually a rather large chunk) of memory is set aside for the System Global Area or SGA. Various Oracle processes manage this area of memory to do any of the following and more: ● Retrieve data from the database and deliver it to user processes (a PL/SQL procedure executing an explicit cursor, an Oracle Forms application querying records through a base table block, an Internet HTML page utilizing the Oracle WebServer interface, and so on). ● Change data and then manage the transaction processing (commits and rollbacks) based on those changes. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. ● Provide access to PL/SQL programs for execution in the server itself. ● Transfer information between Oracle sessions using database pipes and database alerts. When you use a stored program element (by executing a procedure or function or by making reference to a nonexecutable part of a package like a constant or cursor), it must be accessible from the SGA. So when you reference a program element, its compiled version is loaded into the SGA's shared pool, if it is not already present. Then any program data associated with that element is instantiated in your Program Global Area (PGA). At that point, the code can be executed or otherwise used in your session. The next time a session with execute authority on that program element references it, it will already have been loaded and will therefore be available for execution. When the SGA shared pool area fills up, code in the pool will be aged out (that is, room will be made for newly requested programs) on a least-recently-used basis. Programs which are used often will therefore most likely be available immediately upon request. You can also pin programs into shared memory if you want to make certain that they will not be aged out. See Chapter 25, Tuning PL/SQL Applications, for more details on pinning. Note that even if your compiled code is aged out of the SGA, any persistent, package-based data will remain available in your PGA. In other words, code may be swapped out of the SGA, but program data remains and persists for the duration of your session (or until you explicitly request a reinitialization of your schema). Figure 23.1 illustrates a number of the points covered in this section. Figure 23.1: The System Global Area and Program Global Area Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 23.1.4 Key Concepts for Program Execution Here are some basic principles to remember about program execution: ● Compiled PL/SQL code is shared among all users with EXECUTE authority on that code. Usually you will set up your environment so that one account or schema owns all the code for an application. You then grant EXECUTE authority to other users on that code. When any of those schemas runs this code, they are working with the same compiled code. Again, the data instantiated and manipulated within those programs is specific to each connection. ● When you reference any individual element in a package, the entire package is loaded into shared memory. This can be both an advantage and a disadvantage. If you group together (in a package) functionality which is usually executed in "close proximity," then you are more likely to find the program you need in shared memory. This will speed up the completion of your program. On the other hand, suppose that you build some very large packages which contain programs covering a disparate range of functionality. My application needs just one function out of the 100 procedures, functions, and cursors defined. Too bad! My SGA and my PGA must absorb the full punishment of the package (both the room needed for the shared, compiled code and all the package data instantiated in my PGA). ● Program data instantiated within a program is stored in PGA for each user, rather than in the SGA. This means that each user has his own copy of program data. If a procedure declares a PL/SQL table and stuffs it full of 1000 strings, every user who executes that procedure has his own copy of that table and its 1000 strings. The nice thing about this characteristic is that gives you a fair amount of flexibility in finding the delicate balance between those ever- Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. competing resources: CPU and memory. NOTE: The architecture in the multi-threaded server (MTS) is a bit different, but the principle is the same: different users have their own copies of their program data. ● Stored code runs under the authority of that code's owner, not that of the schema which is executing the code. Suppose that you have stored all the code for your order entry application in the SYSTEM account (a very bad idea, as this example will illustrate). You then grant EXECUTE authority on that code to SCOTT, the traditional Oracle demonstration account, which has very little power outside of doing whatever it wants with the emp and dept tables. Now suppose further that the delall procedure of the ordent package allows you to delete all orders from the application table. The intention is that only administrators will have the ability to do that. In fact, the only account that can delete from the orders table at all is SYSTEM. Once you have granted EXECUTE authority on ordent to SCOTT, however, all heck can very decidedly break loose. For when a user logged in as SCOTT executes the ordent.delall procedure, that user is, for that moment, acting as though she were connected to SYSTEM. All rows are removed from the orders table! You must, consequently, very careful about (a) the authority of the schema owning your shared application code, and (b) to whom you grant EXECUTE authority on that code. ● Even though stored code runs under the authority of that code's owner, the USER function still returns the name of the schema currently connected to Oracle. The USER function does not, in other words, return the name of the schema which owns the code in which the USER function was called. Previous: 22.7 Tips for Parameter Design Oracle PL/SQL Programming, 2nd Edition Next: 23.2 Transaction Integrity and Execute Authority 22.7 Tips for Parameter Design Book Index 23.2 Transaction Integrity and Execute Authority The Oracle Library Navigation Copyright (c) 2000 O'Reilly & Associates. All rights reserved. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Previous: 23.1 Executing Stored Code Chapter 23 Managing Code in the Database Next: 23.3 Module Validation and Dependency Management 23.2 Transaction Integrity and Execute Authority The RDBMS and SQL languages give you the capability to tightly control access to and changes in any particular table. With the GRANT command you can, for example, make sure that only certain roles and users have the ability to perform an UPDATE on a given table. This GRANT statement cannot, on the other hand, make sure that the UPDATEs performed by a user or application are done correctly. In a typical banking transaction, you might need to transfer funds from account A to account B. The balance of account B must be incremented, and that of account A decremented. Table access is necessary, but not sufficient, to guarantee that both of these steps are always performed by all programmers who write code to perform a transfer. Without stored objects, the best you can do is require extensive testing and code review to make sure that all transactions are properly constructed. With stored objects, on the other hand, you can guarantee that a funds transfer either completes successfully or is completely rolled back, regardless of who executes the process. 23.2.1 Execute Authority on Stored Objects The secret to achieving this level of transaction integrity is the concept of execute authority (also known as run authority). Instead of granting to a role or user the authority to update a table, you grant privileges to that role/user only to execute a procedure. This procedure controls and provides access to the underlying data structures (see Figure 23.2). The procedure is owned by a separate Oracle RDBMS account, which in turn is granted the actual update privileges on those tables needed to perform the transaction. The procedure therefore becomes the gatekeeper for the transfer transaction. The only way a program (whether an Oracle Forms application or a Pro*C executable) can execute the transfer is through the procedure, so the transaction integrity can be guaranteed. Figure 23.2: Transaction integrity with a PL/SQL code layer Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. In order for a stored procedure or package to compile (which occurs at the time of creation or replacement), the owner of that program must explicitly be granted all the necessary privileges to any objects referenced by the program. These privileges may not be granted simply to a role. If, for example, procedure disp_customer issues a SELECT statement against the customer table, then the owner of disp_customer must be granted a minimum of SELECT privileges on that table with an explicit command: GRANT privilege ON customer TO procedure_owner; Requiring direct grants to individual Oracle users sometimes causes difficulty in environments where grants are controlled carefully and efficiently through the use of roles. After all, the whole idea of the role is to allow DBAs to move away from the onerous task of directly granting privileges to a myriad of individual users. Yet every one of those users must execute the stored procedures underlying an application. What's a DBA to do? In some Oracle shops, a single account (user), which I'll call STOROBJ, is created in the production environment. This user owns all stored objects and has update privileges on all tables, as is appropriate. Other people who use the applications might have SELECT privileges on a number of tables, and perhaps even update privileges on certain tables that are maintained through Oracle Forms applications. But all complex transactions are bundled into stored procedures and stored functions, and users are granted EXECUTE authority only to those stored programs. If an Oracle Forms screen needs to perform a funds transfer, it calls the stored procedure and displays confirmation information on the screen. The logic and authority would, however, reside in the database and be controlled tightly by the STOROBJ account. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. [...]... purchase PDF Split-Merge on www.verypdf.com to remove this watermark Previous: 23.2 Transaction Integrity and Execute Authority 23.2 Transaction Integrity and Execute Authority Oracle PL/SQL Programming, 2nd Edition Book Index Next: 23.4 Remote Procedure Calls 23.4 Remote Procedure Calls The Oracle Library Navigation Copyright (c) 2000 O'Reilly & Associates All rights reserved Please purchase PDF Split-Merge... returned to the local program Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Previous: 23.3 Module Validation and Dependency Management 23.3 Module Validation and Dependency Management Oracle PL/SQL Programming, 2nd Edition Book Index Next: 23.5 Managing Stored Objects with SQL*Plus 23.5 Managing Stored Objects with SQL*Plus The Oracle Library Navigation Copyright (c) 2000... Previous: 23.4 Remote Procedure Calls 23.4 Remote Procedure Calls Oracle PL/SQL Programming, 2nd Edition Book Index Next: 23.6 Using SQL to Examine Stored Objects 23.6 Using SQL to Examine Stored Objects The Oracle Library Navigation Copyright (c) 2000 O'Reilly & Associates All rights reserved Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Previous: 23.5 Managing Stored... obj_cur; END; Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark If you ever do make changes like this, be sure to recompile all modified programs Previous: 23.5 Managing Stored Objects with SQL*Plus 23.5 Managing Stored Objects with SQL*Plus Oracle PL/SQL Programming, 2nd Edition Book Index Next: 23.7 Encrypting Stored Code 23.7 Encrypting Stored Code The Oracle Library Navigation... directory of the Oracle instance In UNIX, this directory is located at $ORACLE_ HOME/bin In Windows NT, you can cd to c:\OraNT\bin, where "c:" denotes the drive on which Oracle has been installed You will then find in your bin directory a program whose name has this format: wrapNN exe, where NN is the version number of the database So if you have Oracle 7.3 installed, you will Please purchase PDF Split-Merge... object_type from user_objects; OBJECT_TYPE FUNCTION INDEX Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark PACKAGE PACKAGE BODY PROCEDURE SEQUENCE SYNONYM TABLE TRIGGER 9 rows selected You can see that USER_OBJECTS does more than keep track of PL/SQL code You can use USER_OBJECTS to obtain a list of all PL/SQL objects currently in the database I created and ran the following... FORMAT 999999 COLUMN code_size FORMAT 999999 TTITLE 'Size of PL/SQL Objects > 2000 Bytes' SPOOL pssize.lis SELECT name, type, source_size, parsed_size, code_size FROM user_object_size Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark WHERE code_size > 2000 ORDER BY code_size DESC / SPOOL OFF By only looking at PL/SQL objects with more than 2000 bytes, I can focus on the larger... create a synonym for the package Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark itself In effect, synonyms can be used to avoid having to provide the schema name of an object; you cannot use it to avoid specifying the package name in which a program is defined Previous: 23.1 Executing Stored Code 23.1 Executing Stored Code Oracle PL/SQL Programming, 2nd Edition Book Index Next:... Copyright (c) 2000 O'Reilly & Associates All rights reserved Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Previous: 23.6 Using SQL to Examine Stored Objects Chapter 23 Managing Code in the Database Next: 24 Debugging PL/ SQL 23.7 Encrypting Stored Code It's kind of fun to watch a programming language like PL/SQL evolve over time First there was Version 1.0 very useful for... each of these tables either with a DESC command in SQL*Plus or by referring to Appendix B in Oracle Corporations's Oracle7 Server Administrator's Guide The following sections provide some examples of the ways you can use these tables 23.6.1 Displaying Object Dependencies Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark The RDBMS keeps track of dependencies between stored objects . within a PL/SQL block: BEGIN calc_totals; END; Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. You can also execute PL/SQL. from PL/SQL Version 1.1, for more information). From a language like C, you will actually use a precompiler called Pro*C (from Oracle) and embed calls to PL/SQL