Pl_sql Faq - Oracle Faq

  • View
    228

  • Download
    0

Embed Size (px)

Text of Pl_sql Faq - Oracle Faq

  • 8/6/2019 Pl_sql Faq - Oracle Faq

    1/15

    PL/SQL FAQ

    From Oracle FAQ

    PL/SQL FAQ - Oracle's Procedural Language extension to SQL:

    Contents

    1 What is PL/SQL and what is it used for?2 What is the difference between SQL and PL/SQL?

    3 Should one use PL/SQL or Java to code procedures and triggers?

    4 How can one see if somebody modified any code?

    5 How can one search PL/SQL code for a string/ key value?

    6 How does one keep a history of PL/SQL code changes?

    7 How can I protect my PL/SQL source code?

    8 How can I know which stored PL/SQL code is wrapped?

    9 Can one print to the screen from PL/SQL?

    10 Can one read/write files from PL/SQL?

    11 Can one call DDL statements from PL/SQL?

    12 Can one use dynamic SQL statements from PL/SQL?13 What is the difference between %TYPE and %ROWTYPE?

    14 How does one get the value of a sequence into a PL/SQL variable?

    15 Can one execute an operating system command from PL/SQL?

    16 How does one loop through tables in PL/SQL?

    17 How often should one COMMIT in a PL/SQL loop? / What is the best commit strategy?

    18 I can SELECT from SQL*Plus but not from PL/SQL. What is wrong?

    19 What is a mutating and constraining table?

    20 Can one pass an object/table as an argument to a remote procedure?

    21 What is the difference between stored procedures and functions?

    22 Is there a PL/SQL Engine in SQL*Plus?

    23 Is there a limit on the size of a PL/SQL block?24 What are the PL/SQL compiler limits for block, record, subquery and label nesting?

    25 Can one COMMIT/ ROLLBACK from within a trigger?

    What is PL/SQL and what is it used for?

    SQL is a declarative language that allows database programmers to write a SQL declaration and hand it to the

    database for execution. As such, SQL cannot be used to execute procedural code with conditional, iterative and

    QL FAQ - Oracle FAQ http://www.orafaq.com/wiki/PL/S

    5 30/05/20

  • 8/6/2019 Pl_sql Faq - Oracle Faq

    2/15

    sequential statements. To overcome this limitation, PL/SQL was created.

    PL/SQL is Oracle's Procedural Language extension to SQL. PL/SQL's language syntax, structure and data types

    are similar to that of Ada. Some of the statements provided by PL/SQL:

    Conditional Control Statements:

    IF ... THEN ... ELSIF ... ELSE ... END IF;

    CASE ... WHEN ... THEN ... ELSE ... END CASE;

    Iterative Statements:

    LOOP ... END LOOP;

    WHILE ... LOOP ... END LOOP;

    FOR ... IN [REVERSE] ... LOOP ... END LOOP;

    Sequential Control Statements:

    GOTO ...;

    NULL;

    The PL/SQL language includes object oriented programming techniques such as encapsulation, function

    overloading, information hiding (all but inheritance).

    PL/SQL is commonly used to write data-centric programs to manipulate data in an Oracle database.

    Example PL/SQL blocks:

    /* Remember to SET SERVEROUTPUT ON to see the output */

    BEGIN

    DBMS_OUTPUT.PUT_LINE('Hello World');

    END;

    /

    BEGIN

    -- A PL/SQL cursor

    FOR cursor1 IN (SELECT * FROM table1) -- This is an embedded SQL statement

    LOOP

    DBMS_OUTPUT.PUT_LINE('Column 1 = ' || cursor1.column1 ||

    ', Column 2 = ' || cursor1.column2);

    END LOOP;

    END;

    /

    What is the difference between SQL and PL/SQL?Both SQL and PL/SQL are languages used to access data within Oracle databases.

    SQL is a limited language that allows you to directly interact with the database. You can write queries

    (SELECT), manipulate objects (DDL) and data (DML) with SQL. However, SQL doesn't include all the things

    that normal programming languages have, such as loops and IF...THEN...ELSE statements.

    PL/SQL is a normal programming language that includes all the features of most other programming languages.

    But, it has one thing that other programming languages don't have: the ability to easily integrate with SQL.

    QL FAQ - Oracle FAQ http://www.orafaq.com/wiki/PL/S

    5 30/05/20

  • 8/6/2019 Pl_sql Faq - Oracle Faq

    3/15

    Some of the differences:

    SQL is executed one statement at a time. PL/SQL is executed as a block of code.

    SQL tells the database what to do (declarative), not how to do it. In contrast, PL/SQL tell the database

    how to do things (procedural).

    SQL is used to code queries, DML and DDL statements. PL/SQL is used to code program blocks, triggers,

    functions, procedures and packages.

    You can embed SQL in a PL/SQL program, but you cannot embed PL/SQL within a SQL statement.

    Should one use PL/SQL or Java to code procedures and triggers?

    Both PL/SQL and Java can be used to create Oracle stored procedures and triggers. This often leads to

    questions like "Which of the two is the best?" and "Will Oracle ever desupport PL/SQL in favour of Java?".

    Many Oracle applications are based on PL/SQL and it would be difficult of Oracle to ever desupport PL/SQL.

    In fact, all indications are that PL/SQL still has a bright future ahead of it. Many enhancements are still being

    made to PL/SQL. For example, Oracle 9i supports native compilation of Pl/SQL code to binaries. Not to

    mention the numerous PL/SQL enhancements made in Oracle 10g and 11g.

    PL/SQL and Java appeal to different people in different job roles. The following table briefly describes the

    similarities and difference between these two language environments:

    PL/SQL:

    Can be used to create Oracle packages, procedures and triggers

    Data centric and tightly integrated into the database

    Proprietary to Oracle and difficult to port to other database systems

    Data manipulation is slightly faster in PL/SQL than in Java

    PL/SQL is a traditional procedural programming language

    Java:

    Can be used to create Oracle packages, procedures and triggers

    Open standard, not proprietary to Oracle

    Incurs some data conversion overhead between the Database and Java type

    Java is an Object Orientated language, and modules are structured into classes

    Java can be used to produce complete applications

    PS: Starting with Oracle 10g, .NET procedures can also be stored within the database (Windows only).

    Nevertheless, unlike PL/SQL and JAVA, .NET code is not usable on non-Windows systems.

    PS: In earlier releases of Oracle it was better to put as much code as possible in procedures rather than triggers.At that stage procedures executed faster than triggers as triggers had to be re-compiled every time before

    executed (unless cached). In more recent releases both triggers and procedures are compiled when created

    (stored p-code) and one can add as much code as one likes in either procedures or triggers. However, it is still

    considered a best practice to put as much of your program logic as possible into packages, rather than triggers.

    How can one see if somebody modified any code?

    The source code for stored procedures, functions and packages are stored in the Oracle Data Dictionary. One

    QL FAQ - Oracle FAQ http://www.orafaq.com/wiki/PL/S

    5 30/05/20

  • 8/6/2019 Pl_sql Faq - Oracle Faq

    4/15

  • 8/6/2019 Pl_sql Faq - Oracle Faq

    5/15

    be cheating.

    How can I protect my PL/SQL source code?

    Oracle provides a binary wrapper utility that can be used to scramble PL/SQL source code. This utility was

    introduced in Oracle7.2 (PL/SQL V2.2) and is located in the ORACLE_HOME/bin directory.

    The utility use human-readable PL/SQL source code as input, and writes out portable binary object code(somewhat larger than the original). The binary code can be distributed without fear of exposing your

    proprietary algorithms and methods. Oracle will still understand and know how to execute the code. Just be

    careful, there is no "decode" command available. So, don't lose your source!

    The syntax is:

    wrap iname=myscript.pls oname=xxxx.plb

    Please note: there is no legal way to unwrap a *.plb binary file. You are supposed to backup and keep your *.pls

    source files after wrapping them. However it ispossible

    for skilled hackersto unwrap

    your wrapped OraclePL/SQL code.

    How can I know which stored PL/SQL code is wrapped?

    The following query gives the list of all wrapped PL/SQL code:

    select owner, name, type

    from dba_source

    where line = 1

    and instr(text, ' wrapped'||chr(10))+instr(text, ' wrapped '||chr(10)) > 0

    order by 1, 2, 3

    /

    Can one print to the screen from PL/SQL?

    One can use the DBMS_OUTPUT package to write information to an output buffer. This buffer can be

    displayed on the screen from SQL*Plus if you issue the SET SERVEROUTPUT ON; command. For example:

    set serveroutput on

    begin

    dbms_output.put_line('Look Ma, I can print from PL/SQL!!!');

    end;

    /

    DBMS_OUTPUT is useful for debugging PL/SQL programs. However, if you print too much, the output buffer

    will overflow. In that case, set the buffer size to a larger value, eg.: set serveroutput on size 200000

    If you forget to set serveroutput on type SET SERVEROUTPUT ONonce you remember, and thenEXEC

    NULL;. If you haven't cleared the DBMS_OUTPUT buffer with the disable or enable procedure, SQL*Plus will

    display the entire contents of the buffer when it executes this dummy PL/SQL block.

    To display an empty line, it is better to use new_line procedure thanput_line with an empty string.

    QL FAQ - Oracle FAQ http://www.orafaq.com/wiki/PL/S

    5 30/05/20

  • 8/6/2019 Pl_sql Faq - Oracle Faq

    6/15

    Can one read/write files from PL/SQL?

    The UT