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  Late Binding and Runtime Binding in PL/SQL
 

Oracle Tips by Burleson

Late Binding and Runtime Binding in PL/SQL

In the examples so far we have declared variables as a separate object using one of PL/SQL’s standard datatypes. Normally a PL/SQLvariable is closely tied to a database object and uses the same datatype.  For example, if the variable will hold the book title from the book table, the variable definition must be of the exact same type and size as the table column.  But what happens when the DBA changes the book table so that book_title is defined as a varchar2(60) instead of a varchar2(40)?  It’s important to program in such a way that when the tables are changed, the PL/SQL code does not always need to be changed.  To get this independence, Oracle has provided a method to declare a variable using the database object the data is based on.  To execute this use the %type declaration.

v_auth_name author.author_last_name%type;

The above declaration creates a variable called v_auth_name that has the same type definition as the author_last_name column in the author table.  Since the PL/SQL variable is declared when the PL/SQL is executed (a process called “late binding” or “runtime binding”), the variable will always match the type definition of the author_last_name column in the database. In plain English, all changes to the type definition in the database are automatically applied to the PL/SQL variable.  You can also create records using the %rowtype declaration.

r_auth  author%rowtype;

The variable r_auth ( r_ is for record) is declared as a record that will hold one row from the author table.  If the DBA adds a column to the author table in the database, the record r_auth will automatically include the new column.  The PL/SQL block continues to function correctly after the change.  Of course, if my code needs to use the new column, then the code will need to be updated.  The example below selects data from the database and stores it in the variables defined.

SQL> declare
  2    r_auth author%rowtype;
  3    v_last_name author.author_last_name%type;
  4  begin
  5    select * into r_auth
  6    from author
  7    where author_key = 'A101';
  8
  9    select author_last_name into v_last_name
 10    from author
 11    where author_key = 'A101';
 12
 13    dbms_output.put_line ('Name: '||
 14                        r_auth. author_last_name);
 15    dbms_output.put_line ('Name: '||v_last_name);
 16  end;
 17  / 

Name: jones
Name: jones

Notice that if the DBA adds a column to the author table, the block still executes without problem because the row is defined using the %rowtype declaration.  If the DBA changes the size of the author_last_name column, the block picks up the change when the v_last_name variable is declared because it used %type.

The internal variables in a record are accessed using the “dot” notation.  In the example a row was retrieved into the record r_auth.  To get the author last name from the record, use the “record.column_name”.

dbms_output.put_line (‘Name: ‘||
                      r_auth. author_last_name);

Since the record is defined as author%rowtype, it contains an entry for every column in the author table.  If the column is null in the table, it will be null in the record.  Anytime variables interact with the data in the database, they should be defined using %type or %rowtype

Follow the link for more information on EXECUTE IMMEDIATE.


The above book excerpt is from:

Easy Oracle PL/SQL Programming

Get Started Fast with Working PL/SQL Code Examples

ISBN 0-9759135-7-3   

John Garmany 

http://www.rampant-books.com/book_2005_1_easy_plsql.htm

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