Oracle extract schema tips

Oracle Database Tips by Donald Burleson

About Oracle schema extraction

Oracle professionals must frequently "punch," or extract, table and index definitions from Oracle and move them to different systems. Extracting Data Definition Language (DDL) for Oracle schema objects (e.g., tables, indexes, stored procedures, triggers, sequences, etc.) from the dictionary is very useful when you're migrating a system to a new platform and you want to pre-create the objects in a new tablespace.

Generally, in an Oracle migration, the schema and DDL are created in the target database, and then the rows are imported into the new database using the Oracle imp utility with the IGNORE=Y parameter. The IGNORE=Y parameters tells Oracle to use the new DDL definitions instead of the DDL inside the import data file.

But in Oracle9i and beyond, you can use the new utility package called dbms_metadata that will easily display DDL and stored procedures directly from the data dictionary. Using this powerful utility, you can punch individual objects or an entire Oracle schema. Best of all, it is easy to use. You simply execute dbms_metadata.get_ddl, specify the object names, and Oracle will extract ready-to-use DDL.

For large migrations, you can modify the dbms_metadata syntax to punch a whole schema. As you can see in Listing C, it is easily done by selecting dbms_metadata. get_ddl and specifying USER_TABLES and USER_INDEXES. This syntax will punch all table and index definitions for the entire schema.

This exercise will allow you to view the important statistics that are gathered within the Oracle database. Your first task is to analyze your pubs schema. To do this, you must "analyze" all of the tables and indexes in the database. For example, and analyze command for the authors table might look like this:

analyze table authors compute statistics;

Now, after having analyzed your schema, rerun the query from the previous step, and note the changes in the statistics. Contrast your personal findings with the topics in the reading "What is your optimizer philosophy?", and discuss how often it is "necessary" to re-analyze a schema for the cost-based optimizer. Post your thoughts and notes in the discussion forum.

The query below will extract all of the schema names from the Oracle data dictoinary.

select distinct
   (owner)
from
   dba_segments
where
   owner in
   (select username
    from dba_users
    where default_tablespace not in ('SYSTEM','SYSAUX')
)
;

or

select distinct(owner) from dba_segments
where owner not in (
'SYSTEM',
'XDB',
'SYS',
'TSMSYS',
'MDSYS',
'EXFSYS',
'WMSYS',
'ORDSYS',
'OUTLN',
'DBSNMP'
);

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