Creating Dynamic Oracle Tables Without Pre-Defined Types: A Flexible Approach to Data-Driven Applications

Creating Dynamic Oracle Tables Without Pre-Defined Types

In this blog post, we will explore how to create dynamic Oracle tables without pre-defined types. This can be useful in scenarios where the schema is forbidden to change or when you need to create a table on the fly based on user input.

Background and Limitations of Oracle’s Dynamic Table Creation

Oracle’s PL/SQL language has several features that make it suitable for developing complex applications, including support for user-defined types. However, this same feature can also be a hindrance in certain situations, such as when you need to create a table without pre-defining its structure.

In standard SQL, you can use the VALUES row constructor to create dynamic tables. This approach is supported by most databases and allows you to define the columns and their data types inline with your query. However, Oracle has some limitations in this regard.

Using Oracle’s Built-in DUAL Table

One workaround for creating dynamic tables without pre-defined types in Oracle is to use a combination of the DUAL table and the UNION ALL operator.

The DUAL table is a special table in Oracle that contains only one row with two columns, both of which are identical. You can use this table as a source for your dynamic rows by selecting specific values and then combining them using UNION ALL.

Here’s an example:

select 'att1' as attr from dual
union all
select 'att2' as attr from dual
union all
select 'att3' as attr from dual
union all
select 'att4' as attr from dual;

This will create a table with four rows, each containing one of the specified attribute names.

Adding More Columns

To add more columns to your dynamic table, you can simply select additional values and combine them using UNION ALL. For example:

select 'att11' as attr1, 'att12' as attr2 from dual
union all
select 'att21' as attr1, 'att22' as attr2 from dual;

This will create a table with two rows and two columns each.

Using Heterogeneous Columns

If you need to work with heterogeneous data types (i.e., different data types for each column), you’ll need to use Oracle’s advanced features like PL/SQL tables, arrays, or collections.

For example, if you have a set of values that require different data types, such as integers and strings, you can create a table with columns of varying data types:

create type int_array is array<int>;
create type str_array is array<varchar2(255)>;

declare
  v_int_array int_array := int_array(1, 2, 3);
  v_str_array str_array := str_array('hello', 'world');

begin
  for i in v_int_array.first..v_int_array.last loop
    dbms_output.put_line(i);
  end loop;
  
  for i in v_str_array first..v_str_array last loop
    dbms_output.put_line(i);
  end loop;
end;

This code creates two arrays, one of integers and one of strings, and then loops through each element to print it out.

Conclusion

Creating dynamic Oracle tables without pre-defined types can be achieved using a combination of the DUAL table and the UNION ALL operator. This approach allows you to create tables with varying numbers of rows and columns, making it suitable for complex applications where schema changes are not allowed.

While this approach has its limitations, it provides a powerful solution for working with dynamic data in Oracle databases. By understanding how to use Oracle’s built-in features like DUAL and UNION ALL, you can create flexible and efficient solutions for your most challenging data-driven tasks.