|SQL*Plus User's Guide and Reference
Learning SQL*Plus Basics, 3 of 4
Your computer's cursor, or pointer (typically an underline, a rectangular block, or a slash), appears after the command prompt. The cursor indicates the place where the next character you type will appear on your screen.
To tell SQL*Plus what to do, simply type the command you wish to enter. Usually, you separate the words in a command from each other by a space or tab. You can use additional spaces or tabs between words, if you wish, to make your commands more readable.
You will see examples of spacing and indentation throughout this Guide. When you enter the commands in the exercises, you do not have to space them as shown, but you may find them clearer to read if you do.
You can enter commands in capitals or lowercase. For the sake of clarity, all table names, column names, and commands in this Guide appear in capital letters.
You can enter three kinds of commands at the command prompt:
The manner in which you continue a command on additional lines, end a command, or execute a command differs depending on the type of command you wish to enter and run. Examples of how to run and execute these types of commands are found on the following pages.
To get online help for SQL*Plus commands, type HELP at the command prompt followed by the name of the command. For example:
After you enter the command and direct SQL*Plus to execute it, SQL*Plus processes the command and re-displays the command prompt, indicating that you can enter another command.
The SQL command language enables you to manipulate data in the database. See your Oracle8i SQL Reference for information on individual SQL commands.
In this example, you will enter and execute a SQL command to display the employee number, name, job, and salary of each employee in the sample table EMP.
If you make a mistake, use [Backspace] to erase it and re-enter. When you are done, press [Return] to move to the next line.
The semicolon (;) means that this is the end of the command. Press [Return]. SQL*Plus processes the command and displays the results on the screen:
EMPNO ENAME JOB SAL ----- ---------- ------------ ------ 7369 SMITH CLERK 800 7499 ALLEN SALESMAN 1600 7521 WARD SALESMAN 1250 7654 MARTIN SALESMAN 1250 7782 CLARK MANAGER 2450 7844 TURNER SALESMAN 1500 7876 ADAMS CLERK 1100 7900 JAMES CLERK 800 7934 MILLER CLERK 1300 9 rows selected SQL>
After displaying the results and the number of rows retrieved, SQL*Plus displays the command prompt again. If you made a mistake and therefore did not get the results shown above, simply re-enter the command.
The headings may be repeated in your output, depending on the setting of a system variable called PAGESIZE. Whether you see the message concerning the number of records retrieved depends on the setting of a system variable called FEEDBACK. You will learn more about system variables later in this chapter in the section "Variables that Affect Running Commands". To save space, the number of records selected will not be shown in the rest of the examples in this Guide.
Just as spoken language has syntax rules that govern the way we assemble words into sentences, SQL*Plus has syntax rules that govern how you assemble words into commands. You must follow these rules if you want SQL*Plus to accept and execute your commands.
You can divide your SQL command into separate lines at any points you wish, as long as individual words are not split between lines. Thus, you can enter the query you entered in Example 2-3 on one line:
You can also enter the query on several lines:
In this Guide, you will find most SQL commands divided into clauses, one clause on each line. In Example 2-3, for instance, the SELECT and FROM clauses were placed on separate lines. Many people find this most convenient, but you may choose whatever line division makes your command most readable to you.
You can end a SQL command in one of three ways:
A semicolon (;) tells SQL*Plus that you want to run the command. Type the semicolon at the end of the last line of the command, as shown in Example 2-3, and press [Return]. SQL*Plus will process the command and store it in the SQL buffer (see the section "The SQL Buffer" below for details). If you mistakenly press [Return] before typing the semicolon, SQL*Plus will prompt you with a line number for the next line of your command. Type the semicolon and press [Return] again to run the command.
A slash (/) on a line by itself also tells SQL*Plus that you wish to run the command. Press [Return] at the end of the last line of the command. SQL*Plus prompts you with another line number. Type a slash and press [Return] again. SQL*Plus will execute the command and store it in the buffer (see the section "The SQL Buffer" below for details).
A blank line tells SQL*Plus that you have finished entering the command, but do not want to run it yet. Press [Return] at the end of the last line of the command. SQL*Plus prompts you with another line number.
Press [Return] again; SQL*Plus now prompts you with the SQL*Plus command prompt. SQL*Plus does not execute the command, but stores it in the SQL buffer (see the section "The SQL Buffer" below for details). If you subsequently enter another SQL command, SQL*Plus overwrites the previous command in the buffer.
Stored procedures are PL/SQL functions, packages, or procedures. To create stored procedures, you use SQL CREATE commands. The following SQL CREATE commands are used to create stored procedures:
Entering any of these commands places you in PL/SQL mode, where you can enter your PL/SQL subprogram. For more information, see the section "Running PL/SQL Blocks" in this chapter). When you are done typing your PL/SQL subprogram, enter a period (.) on a line by itself to terminate PL/SQL mode. To run the SQL command and create the stored procedure, you must enter RUN or slash (/). A semicolon (;) will not execute these CREATE commands.
When you use CREATE to create a stored procedure, a message appears if there are compilation errors. To view these errors, you use SHOW ERRORS. For example:
To execute a PL/SQL statement that references a stored procedure, you can use the EXECUTE command. EXECUTE runs the PL/SQL statement that you enter immediately after the command. For example:
The area where SQL*Plus stores your most recently entered SQL command or PL/SQL block is called the SQL buffer. The command or block remains there until you enter another. Thus, if you want to edit or re-run the current SQL command or PL/SQL block, you may do so without re-entering it. For more information about editing or re-running a command or block stored in the buffer see the section "Running Command Files" in Chapter 3.
SQL*Plus does not store the semicolon or the slash you type to execute a command in the SQL buffer.
You can run (or re-run) the current SQL command or PL/SQL block by entering the RUN command or the slash (/) command at the command prompt. The RUN command lists the SQL command or PL/SQL block in the buffer before executing the command or block; the slash (/) command simply runs the SQL command or PL/SQL block.
You can also use PL/SQL subprograms (called blocks) to manipulate data in the database. See your PL/SQL User's Guide and Reference for information on individual PL/SQL statements.
To enter a PL/SQL subprogram in SQL*Plus, you need to be in PL/SQL mode. You are placed in PL/SQL mode when
SQL*Plus treats PL/SQL subprograms in the same manner as SQL commands, except that a semicolon (;) or a blank line does not terminate and execute a block. Terminate PL/SQL subprograms by entering a period (.) by itself on a new line.
SQL*Plus stores the subprograms you enter at the SQL*Plus command prompt in the SQL buffer. Execute the current subprogram by issuing a RUN or slash (/) command. Likewise, to execute a SQL CREATE command that creates a stored procedure, you must also enter RUN or slash (/). A semicolon (;) will not execute these SQL commands as it does other SQL commands.
SQL*Plus sends the complete PL/SQL subprogram to Oracle for processing (as it does SQL commands). See your PL/SQL User's Guide and Reference for more information.
You might enter and execute a PL/SQL subprogram as follows:
SQL> DECLARE 2 x NUMBER := 100; 3 BEGIN 4 FOR i IN 1..10 LOOP 5 IF MOD (i, 2) = 0 THEN --i is even 6 INSERT INTO temp VALUES (i, x, 'i is even'); 7 ELSE 8 INSERT INTO temp VALUES (i, x, 'i is odd'); 9 END IF; 10 x := x + 100; 11 END LOOP; 12 END; 13 . SQL> /
When you run a subprogram, the SQL commands within the subprogram may behave somewhat differently than they would outside the subprogram. See your PL/SQL User's Guide and Reference for detailed information on the PL/SQL language.
You can use SQL*Plus commands to manipulate SQL commands and PL/SQL blocks and to format and print query results. SQL*Plus treats SQL*Plus commands differently than SQL commands or PL/SQL blocks. For information on individual SQL*Plus commands, refer to the "Command Reference" in Chapter 8.
To speed up command entry, you can abbreviate many SQL*Plus commands to one or a few letters. Abbreviations for some SQL*Plus commands are described along with the commands in Chapters 3, 4, and 6. For abbreviations of all SQL*Plus commands, refer to the "Command Reference" in Chapter 8.
This example shows how you might enter a SQL*Plus command to change the format used to display the column SAL of the sample table EMP.
If you make a mistake, use [Backspace] to erase it and re-enter. When you have entered the line, press [Return]. SQL*Plus notes the new format and displays the SQL*Plus command prompt again, ready for a new command.
SQL> RUN 1 SELECT EMPNO, ENAME, JOB, SAL 2* FROM EMP WHERE SAL < 2500 EMPNO ENAME JOB SALARY ----- ------------- ------------ ------ 7369 SMITH CLERK $800 7499 ALLEN SALESMAN $1,600 7521 WARD SALESMAN $1,250 7654 MARTIN SALESMAN $1,250 7782 CLARK MANAGER $2,450 7844 TURNER SALESMAN $1,500 7876 ADAMS CLERK $1,100 7900 JAMES CLERK $800 7934 MILLER CLERK $1,300
The COLUMN command formatted the column SAL with a dollar sign ($) and a comma (,) and gave it a new heading. The RUN command then re-ran the query of Example 2-3, which was stored in the buffer. SQL*Plus does not store SQL*Plus commands in the SQL buffer.
SQL*Plus commands have a different syntax from SQL commands or PL/SQL blocks.
You can continue a long SQL*Plus command by typing a hyphen at the end of the line and pressing [Return]. If you wish, you can type a space before typing the hyphen. SQL*Plus displays a right angle-bracket (>) as a prompt for each additional line.
Since SQL*Plus identifies the hyphen as a continuation character, entering a hyphen within a SQL statement will be ignored by SQL*Plus. SQL*Plus will not identify the statement as a SQL statement until after the input processing has joined the lines together and removed the hyphen. For example, entering the following will return an error:
SQL> select 200 - > 100 from dual; select 200 100 from dual * ERROR at line 1: ORA-00923: FROM keyword not found where expected
To ensure that the statement is interpreted correctly, move the hyphen from the end of the line.
You do not need to end a SQL*Plus command with a semicolon. When you finish entering the command, you can just press [Return]. If you wish, however, you can enter a semicolon at the end of a SQL*Plus command.
The SQL*Plus command SET controls many variables--called system variables--the settings of which affect the way SQL*Plus runs your commands. System variables control a variety of conditions within SQL*Plus, including default column widths for your output, whether SQL*Plus displays the number of records selected by a command, and your page size. System variables are also called SET command variables.
The examples in this Guide are based on running SQL*Plus with the system variables at their default settings. Depending on the settings of your system variables, your output may appear slightly different than the output shown in the examples. (Your settings might differ from the default settings if you have a SQL*Plus LOGIN file on your computer.)
For more information on system variables and their default settings, see the SET command in Chapter 8. For details on the SQL*Plus LOGIN file, refer to the section "Setting Up Your SQL*Plus Environment" under "Saving Commands for Later Use" in Chapter 3 and to the SQLPLUS command in Chapter 7.
To list the current setting of a SET command variable, enter SHOW followed by the variable name at the command prompt. See the SHOW command in Chapter 8 for information on other items you can list with SHOW.
Through the SQL DML commands UPDATE, INSERT, and DELETE--which can be used independently or within a PL/SQL block--specify changes you wish to make to the information stored in the database. These changes are not made permanent until you enter a SQL COMMIT command or a SQL DCL or DDL command (such as CREATE TABLE), or use the autocommit feature. The SQL*Plus autocommit feature causes pending changes to be committed after a specified number of successful SQL DML transactions. (A SQL DML transaction is either an UPDATE, INSERT, or DELETE command, or a PL/SQL block.)
You control the autocommit feature with the SQL*Plus SET command's AUTOCOMMIT variable. It has these four forms:
Turns autocommit on.
Turns autocommit off (the default).
Commits changes after n SQL commands or PL/SQL blocks.
Turns autocommit on.
To turn the autocommit feature on, enter
Alternatively, you can enter the following to turn the autocommit feature on:
Until you change the setting of AUTOCOMMIT, SQL*Plus will automatically commit changes from each SQL command or PL/SQL block that specifies changes to the database. After each autocommit, SQL*Plus displays the following message:
When the autocommit feature is turned on, you cannot roll back changes to the database.
To commit changes to the database after a number of SQL DML commands or PL/SQL blocks, for example, ten, enter
SQL*Plus counts SQL DML commands and PL/SQL blocks as they are executed and commits the changes after the tenth SQL DML command or PL/SQL block.
For this feature, a PL/SQL block is regarded as one transaction, regardless of the actual number of SQL commands contained within it.
To turn the autocommit feature off again, enter the following command:
To confirm that AUTOCOMMIT is now set to OFF, enter the following SHOW command:
Suppose you have displayed the first page of a 50 page report and decide you do not need to see the rest of it. Press [Cancel]. (Refer to Table 2-1 at the beginning of this chapter to see how [Cancel] is labelled on your keyboard.) SQL*Plus will stop the display and return to the command prompt.
Pressing [Cancel] will not stop the printing of a file that you have sent to a printer with the OUT clause of the SQL*Plus SPOOL command. (You will learn about printing query results in Chapter 4.) You can stop the printing of a file through your operating system. For more information, see your operating system's installation and user(s) manual.
Use the SQL*Plus command TIMING to collect and display data on the amount of computer resources used to run one or more commands or blocks. TIMING collects data for an elapsed period of time, saving the data on commands run during the period in a timer.
To delete all timers, enter CLEAR TIMING at the command prompt.
You can execute a host operating system command from the SQL*Plus command prompt. This is useful when you want to perform a task such as listing existing host operating system files.
To run a host operating system command, enter the SQL*Plus command HOST followed by the host operating system command. For example, this SQL*Plus command runs a host command, DIRECTORY *.SQL:
When the host command finishes running, the SQL*Plus command prompt appears again.