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ddl

Take care with automatic indexes

This one came in via an AskTOM question. You need to be careful when disabling constraints that are underpinned by an index, especially when it comes to the storage for that index.

Let’s take a look at a simple example. I’ll explicitly nominate the LARGETS tablespace for my index that will support the primary key.

Grab all the DDL

I posted a video a couple of days ago showing a trigger mechanism to customize the capture of DDL that is issued on your database. The aim here is to be more generous with letting developers execute DDL on their Development databases, whilst still having a thorough record of the changes that are occurring. Of course, it goes without saying, which is why I am saying it </p />
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DDL for constraints – subtle things

The DBMS_METADATA package is very cool. I remember the days of either hand-crafting DDL statements based on queries to the data dictionary, or many a DBA will be familiar with running “imp show=y” or “imp indexfile=…” in order to then laboriously extract the DDL required from the import log file.  DBMS_METADATA removed all of those annoyances to give us a simple API to get the true and complete DDL for a database object.

But when extracting DDL from the database using the DBMS_METADATA package, you need to be aware of some subtleties especially if you plan on executing that DDL in the database.

Better to be safe than sorry…

I’ve always been worried about taking a script that is fine to run in my non-production environments (in particular a DROP script) and accidentally running it in a Production environment, shortly followed by the typing up of a fresh resume to look for a new job once the mistake is discovered Smile

DDL triggers – interesting results

This question came in on AskTom, yielding a very interesting result when it comes to DDL triggers. To set the scene, I’ll first create a table called T which is just a copy of SCOTT.EMP

Duplicate constraints are impossible right ?

Here’s a very simple example of a table called PARENT being a (surprise surprise) parent in a referential integrity relationship to a (drum roll for my choice of name) CHILD table


SQL> create table parent ( p int, constraint PAR_PK primary key (p) );

Table created.

SQL> create table child ( c int,
  2        p int
  3      );

Table created.

SQL> alter table child add constraint fk1 foreign key ( p ) references parent ( p );

Table altered.

That is all as we would expect, and similarly, if I inadvertently try to add the same foreign key constraint, I’ll get an error