Unveiling the Mystery: Extracting Object DDL in Oracle Database (9i onwards)

Ever faced the situation where you needed the Data Definition Language (DDL) script for an existing table, view, or other database object in your Oracle database (version 9i or later)? This can be crucial for various tasks, such as replicating schema structures, documenting changes, or troubleshooting issues. Fear not, for Oracle provides a powerful built-in function, DBMS_METADATA.GET_DDL, that empowers you to retrieve the DDL script for virtually any database object. This article delves into the purpose, breakdown, and key points of the provided Oracle code snippet, offering insights and explanations to equip you with the knowledge to effectively extract object DDLs in your Oracle environment.

This command get an objects ddl (9i onwards)

Parameters: OBJECT_TYPE, OBJECT_NAME, SCHEMA

Sample SQL Command

1set pagesize 0
2set long 90000
3select dbms_metadata.get_ddl('TABLE','TABLE_A','ANDY') from dual;

Purpose: Unveiling the Creation Script

The primary purpose of the presented code snippet is to retrieve the DDL script that defines a specific database object within your Oracle database (version 9i onwards). This script encapsulates the commands used to create the object, including details like column definitions, constraints, indexes, and more. Having access to the DDL script provides several benefits:

• Schema Replication: Easily recreate the same database object structure on a different database by executing the retrieved DDL script.
• Documentation and Maintenance: Maintain a clear record of how your database objects were created, facilitating understanding and future modifications.
• Troubleshooting: Analyze the DDL script to pinpoint potential issues with object definitions or configurations.

Breakdown: Decoding the Code

Let's dissect the code line by line, understanding the functionalities of each component:

1. set pagesize 0: This line sets the SQL*Plus output buffer size to zero. The default behavior paginates query results into manageable chunks, which can be inconvenient when retrieving long DDL scripts. Setting pagesize to zero ensures the entire script is returned without interruption.

2. set long 90000: This line adjusts the maximum length allowed for character data types within the current SQL*Plus session. DDL scripts for complex objects can potentially exceed the default limit. By setting long to a higher value (like 90000), we accommodate longer DDL statements.

3. select dbms_metadata.get_ddl('TABLE','TABLE_A','ANDY') from dual: This is the heart of the code. Here's what each element signifies:

   • select: Keyword that initiates the SQL statement.
   • dbms_metadata.get_ddl: This function, part of the DBMS_METADATA package, is specifically designed to retrieve DDL for database objects.
   • 'TABLE': This argument specifies the type of object we want the DDL for (e.g., 'TABLE', 'VIEW', 'PROCEDURE').
   • 'TABLE_A': This argument denotes the actual name of the object for which we're extracting the DDL script.
   • 'ANDY': This argument represents the schema where the object resides.

4. from dual: The from dual clause is a syntactic requirement in this context. dual is a virtual table in Oracle with a single row and one column, serving as a placeholder to complete the SQL statement structure.

Key Points and Considerations

Here are some key points and considerations to remember when using this code:

• Object Type Flexibility: The dbms_metadata.get_ddl function can be used to retrieve DDL for various object types, not just tables. Replace 'TABLE' with the appropriate object type code (e.g., 'VIEW', 'PROCEDURE', 'SEQUENCE').
• Object Permissions: To successfully execute this code, you'll need privileges to access the target object and the DBMS_METADATA package.
• Schema Awareness: Specify the correct schema name ('ANDY' in this example) where the object resides. If unsure, use USER to retrieve the DDL for objects in your own schema.
• Output Formatting: The retrieved DDL script might not be perfectly formatted for readability. You can utilize tools like SQL*Plus formatting commands or external code editors for better presentation.

Insights and Explanations

By leveraging the DBMS_METADATA.GET_DDL function, you gain valuable insights into the underlying structure of your database objects. The retrieved DDL script reveals details like:

• Column Definitions: Data types, lengths, nullability constraints, and default values for all columns within the object.
• Constraints: Primary key, foreign key, check, and unique constraints defined on the object