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Database Interaction with PL/SQL: Nested Tables

This series has been focusing on database interactions with Oracle PL/SQL. Having just covered OBJECT TYPE in Oracle and both SQL and PL/SQL ways of working with OBJECTs in the last article, we will now learn about using NESTED TABLE with OBJECT TYPES from both SQL and PL/SQL point of views. We will also discuss FOR loops with an inline SELECT statement. This article is the fifth in this series.

  1. Database Interaction with PL/SQL: Nested Tables
  2. Working with DML statements using NESTED TABLE with OBJECT TYPE
  3. Working with PL/SQL using NESTED TABLE with OBJECT TYPE
  4. A Powerful FOR loop in PL/SQL
By: Jagadish Chatarji
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June 21, 2005

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Please note that all the examples in this series have been tested only with Oracle 10g.  I didn’t really test them with all the previous versions of Oracle.  I suggest you to refer the documentation of respective version you are using, if any of the programs failed to execute.


Part-3 of my series covered NESTED TABLE a bit and part-4 introduced the concept of OBJECT TYPE.  Now, we shall combine those two in this article.  Let us prepare scripts from scratch to discuss them in detail.  Consider the following:

    CompanyName    varchar2(20),
    Position       varchar2(20),
    NoOfYears      number(2)

The above script just creates an OBJECT TYPE (which is almost similar to the one present in part-4). 

CREATE TYPE t_experience_tbl AS TABLE OF t_experience;

If we observe the above carefully, we are still creating another TYPE (not a concrete table), but it is of TABLE TYPE within database.  For our convenience, I named it as ‘t_experience_tbl’.

CREATE TABLE employees
    Name            varchar2(20),
Experiences     t_experience_tbl
NESTED TABLE Experiences STORE AS Experiences_tab;

The above statement creates a new table ‘employees’ (make sure to drop an old one if it exists) with only two fields,  ‘name’ and ‘experiences’.  The field ‘Experiences’ is created based on the TABLE TYPE ‘t_experience_tbl’.  This means that every employee can now store his experience list in the same row.  Indirectly, experience list itself is a table of information (CompanyName, Position, NoOfYears).  This table is being stored as a part of single row in the table ‘employees’, which is what the NESTED TABLE is.

Even though the NESTED TABLE is logically part of the ‘employees’ table, it is stored externally (with a different table name ‘experiences_tab’) from the main table.  The following statement inserts a row into that table.

insert into employees values
        t_experience('abc company','Software Engineer',3),
        t_experience('xyz company','System Analyst',2),
        t_experience('mnp company','Research fellow',4)

Better not confuse ourselves with the example above.  ‘t_experience_tbl’ is a TABLE TYPE based on ‘t_experience’ OBJECT TYPE.  So, ‘t_experience_tbl’ can have any number of OBJECTs of TYPE ‘t_experience’.  The same concept is practiced above.  And you can insert any number of experiences for a single row.

>>> More Oracle Articles          >>> More By Jagadish Chatarji

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