Learning the Basics of PL/SQL - Page 4

Executing PL/SQL Using Developer 2000's Procedure Builder

Procedure Builder is part of Oracle's Developer 2000 development environment. It allows you to develop and debug PL/SQL program units for use in Developer 2000 applications. With Developer 2000, PL/SQL is used on the client to program the behavior behind the forms, reports, and menus that you develop. You end up with a PL/SQL engine on the client as well as on the server. A nice benefit of this is that Procedure Builder can be used to execute PL/SQL code without having to be connected to a database.

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Note - Many of the advanced features discussed later in this book are available only when executing PL/SQL code in the database.

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Starting Procedure Builder

If you have Developer 2000 installed, you start Procedure Builder by selecting Start, Programs, Developer 2000 R2.0, Procedure Builder. The opening screen is shown in Figure 1.5 and is divided into three sections.

Procedure Builder's opening screen.
(Click for full size)

As you can see, the Procedure Builder window is divided into three major parts. The Object Navigator window allows you to navigate through the various program units, PL/SQL libraries, and database objects to which you have access. The other two parts of the display combine to make up the PL/SQL Interpreter window. The top pane is used when debugging PL/SQL code and shows the code being debugged. The bottom pane is where you can type in and execute ad-hoc PL/SQL blocks.

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New Term - PL/SQL may be used to write procedures, functions, package bodies, package types, and triggers. These constructs are referred to as program units.

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Using Interactive PL/SQL

The PL/SQL interpreter allows you to enter a PL/SQL anonymous block and have it executed. The small block in Listing 1.2, that you typed in earlier, is one such anonymous block. You can type that block into Procedure Builder and execute it, but first you need to make one small change. The code shown in Listing 1.2 contains the following two calls to DBMS_OUTPUT:

dbms_output.put_line('The variable X = ');
dbms_output.put_line(x);

DBMS_OUTPUT is a package that only exists within the database server. Procedure Builder will return errors if you try to execute the code as it stands now. Fortunately, Oracle has a package similar to DBMS_OUTPUT that can be used in its place when you are executing code on a client. The name of that package is TEXT_IO, and it also contains an entry point named PUT_LINE. Take the code shown in Listing 1.2, replace the calls to DBMS_OUTPUT.PUT_LINE with TEXT_IO.PUT_LINE, and you have the code shown in Listing 1.6. This code will run from Procedure Builder.

Listing 1.6 A PL/SQL Block Using TEXT_IO That Will Run from Procedure Builder

DECLARE
 x   INTEGER;
BEGIN
 x := 72600;
 text_io.put_line('The variable X = ');
 text_io.put_line(x);
END;

Now, you can take this code and type it into Procedure Builder's PL/SQL Interpreter. The interpreter will automatically execute the block when you finish entering the last line. The results will look like the following:

The variable X =
72600

Procedure Builder has been written specifically to work with PL/SQL. Unlike SQL*Plus, you do not need to enter a forward-slash to tell Procedure Builder that you are done entering a block of PL/SQL.

Creating the SS_THRESH Function

Creating a function (or any other program unit such as a procedure or package) using Procedure Builder requires a bit more than just typing the CREATE FUNCTION statement into the interpreter. To create a function, you need to tell Procedure Builder that you want to create a new program unit. Do this by selecting the File, New, Program Unit menu option. You will see the dialog box shown in Figure 1.6.

Creating a New Program Unit.

This dialog contains radio buttons allowing you to choose the type of program unit that you are creating and also contains a textbox for the program unit's name. Choose Function, type the name SS_THRESH into the textbox, and click OK. You will see a screen similar to that shown in Figure 1.7.

Entering the code for SS_THRESH.

Figure 1.7 shows the function with the code already written. Of course, Procedure Builder does not write the code for you. When Procedure Builder opens this window, it places a skeleton function in the textbox. You have to fill in the details. When you get the code entered the way that you want it, click the Compile button to compile it, and then click the Close button to close the window.

To execute the function that you just created, type the following statement into the PL/SQL interpreter:

TEXT_IO.PUT_LINE(SS_THRESH);

When you execute this statement, Procedure Builder will execute the function and display the following results:

72600

Connecting to a Database

In addition to creating PL/SQL program units on the client, Procedure Builder can also be used to create and execute program units in a database. To do this, you first need to connect to a database. Use the File, Connect menu option to connect to a database. Once you've logged in, you will be able to browse database program units using the Object Navigator. Figure 1.8 shows the program units owned by the user named JEFF.

Program units in the JEFF schema.

To create a stored function or other program unit in the database, follow these steps:

1. Click to highlight the Stored Program Units entry under the user's name.

2. Click the Create Toolbar button.

3. Proceed as you would when creating a local program unit.

Except for having to choose the schema, the process for creating a PL/SQL function in the database is the same as for creating one locally.

Using SQLPlus Worksheet

If you have Enterprise Manager available, consider using SQLPlus Worksheet for the examples in this book. SQLPlus Worksheet is completely compatible with SQL*Plus, and can be used for all the examples in this book. The advantage that SQL*Plus worksheet has over SQL*Plus is in the interface. Rather than type in large blocks of code one line at a time, you can use a text editor-like interface. After you get the code entered the way that you want it, you can click a toolbar button to execute it.

Executing a PL/SQL Block Using SQLPlus Worksheet

Figure 1.9 shows the SQLPlus Worksheet.

The SQLPlus Worksheet.

As you can see, the SQLPlus Worksheet screen is divided into two halves. The upper half is used for the entry and editing of SQL statements and PL/SQL blocks. The lower half is used to display output. The execute toolbar button, the one with the lightning bolt, is used to execute the statements that you have entered in the upper pane.

There are two ways to use SQLPlus Worksheet to execute commands from a file. One way is to use the File, Open menu option to load the contents of a file into the upper pane, and then click the lightning bolt button. The other way is to use the Worksheet, Run Local Script menu option.

Summary

In this chapter you learned a little about PL/SQL, what it is, and why it is used. You know that PL/SQL is Oracle's procedural language extension to SQL, and that you can use it to write procedures and functions that execute on the server.

This chapter also explains the relationship between PL/SQL, SQL, and SQL*Plus. This should give you a good grasp of how PL/SQL fits into the larger Oracle picture.

You wrote your first PL/SQL stored function, which should give you a good feel for the mechanics of programming with PL/SQL.

SQL*Plus is the tool used throughout this book for PL/SQL code examples. SQLPlus Worksheet and Procedure Builder are two other tools that may also be used to write and execute PL/SQL code.

Q & A

17. Where does PL/SQL code execution take place?

1. Usually, execution takes place at the server level. For the examples in this book, that will always be the case. Some Oracle products, such as Developer/2000, also have the capability to execute PL/SQL blocks locally on the client machine.

17. Can I write a complete application with PL/SQL?

1. Generally speaking you cannot, at least not as most people envision an application. For an end-user application, you would still need a tool, such as PowerBuilder or Developer/2000, in order to design screens and generate reports.

17. I executed some PL/SQL code which used dbms_output.put_line() to print some data, but I didn't see anything. How come?

1. You probably forgot to enable the server output option. Use this SQL*Plus command:

   SET SERVEROUTPUT ON

   If you forget that, your PL/SQL output goes to oblivion.

17. I am using Procedure Builder, and I get errors when I try to execute code that contains calls to dbms_output.put_line(). Why?

1. When you use Procedure Builder to execute code locally, you must use text_io.put_line rather than dbms_output.put_line(). If you are using Procedure Builder, and you have connected to a database, you will be able to execute calls to dbms_output.put_line(), but you won't see the results.

Workshop

Use the following workshop to test your comprehension of this chapter and put what you've learned into practice. You'll find the answers to the quiz and exercises in Appendix A, "Answers."

Quiz

1. What tells SQL*Plus to send your PL/SQL code to the Oracle database for execution?

2. What is the fundamental basis of all PL/SQL code?

3. List an advantage of pushing program logic up to the server level.

4. Name three Oracle products that use PL/SQL.

5. What command tells SQL*Plus to display PL/SQL output?

6. Name at least two options for managing your PL/SQL source code.

Exercises

1. If you didn't encounter any errors when compiling your first function, try putting some in on purpose. Then try out the SHOW ERRORS command.

2. Try each of the three ways mentioned in the chapter for managing your source code. Become familiar with the SQL*Plus EDIT command. Try using the @ command or the START command to execute your PL/SQL code from a text file.

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This article is brought to you by Sams Publishing, publisher of Sams Teach Yourself PL/SQL in 21 Days, Second Edition.