I'm new to pluggable databases and am puzzled by the dictionary views DBA_PDBS and V$PDBS. What's the differnence? The documentation is not helpful, either:
V$PDBS displays information about PDBs associated with the current instance.
1
SELECT * FROM v$pdbs;
CON_ID NAME OPEN_MODE ...
2 PDB$SEED READ ONLY
3 XEPDB1 READ WRITE
DBA_PDBS describes PDBs belonging to a given CDB.
2
SELECT * FROM dba_pdbs;
PDB_ID PDB_NAME STATUS ...
2 PDB_SEED NORMAL
3 XEPDB1 NORMAL
Internally, V$PDBS seems to be based on SYS.X$CON, while DBA_PDBS is based on SYS.CONTAINERS$.
There are similar cases with V$DATAFILE vs DBA_DATA_FILES or V$TABLESPACE vs DBA_TABLESPACES: in this case these views data are read from database control files and are likely redundant for restore/recovery purposes (ie when the SYSTEM tablespace is not yet available, DBAxxx views are not there but when database instance needs to work on datafiles and tablespaces). It's likely for the same reason that we have V$PDBS in addition to DBA_PDBS.
Related
I have to drop a table and to create a view with the same fields and name.
How can I get previously all the objects (tables, triggers, procedure, ...) connected to the original table so as to eventually or recompiling either modifying them?
Oracle version 11g
Thanks!
Run such a query; currently, I'm connected as a privileged user who is capable of querying DBA_DEPENDENCIES.
SQL> SELECT owner, name, type
2 FROM dba_dependencies
3 WHERE 1 = 1
4 AND referenced_owner = 'SCOTT'
5 AND referenced_type = 'TABLE'
6 AND referenced_name = 'EMP';
OWNER NAME TYPE
------------------------------ ------------------------------ ------------------
SCOTT TRG_BIU_EMP TRIGGER
MIKE PKG_EMPLOYEE PACKAGE BODY
SQL>
It says that emp table, owned by scott, is referenced by two other objects:
trigger named trg_biu_emp owned by scott
package body named pkg_employee owned by mike
You can also go with all_dependencies and user_dependencies (pay attention to their description! owner column is missing in user_ views), but you'll get fewer and fewer results because both of them contain less information than dba_dependencies.
Therefore, if you don't want to miss something, look everywhere (i.e. dba_ views). If you don't have required privileges, talk to your DBA.
Also, note that such a query won't discover possible references to that object elsewhere, such as front-end applications developed in e.g. Oracle Forms and Reports or Apex or ...
Is it possible to add a metadata field at column-level (in the Oracle Data Dictionary)?
The purpose would be to hold a flag identifying where individual data items in a table have been anonymised.
I'm an analyst (not a DBA) and I'm using Oracle SQL Developer which surfaces (and enables querying of) the COLUMN_NAME, DATA_TYPE, NULLABLE, DATA_DEFAULT, COLUMN_ID, and COMMENTS metadata fields of our Oracle DB (see pic).
I'd be looking to add another metadata field at this level (essentially, to add a second 'COMMENTS' field) to hold the 'Anonymisation' flag, to support easy querying of our flagged-anonymised data.
If it's possible (and advisable / supportable), I'd be grateful for any advice for describing the steps required to enable this, which I can then discuss with our Developer and DBA.
Short answer: NO.
But where could you keep that information?
In your data model.
Oracle provides a free data modeling solution, Oracle SQL Developer Data Modeler. It provides the ability to mark table/view columns as sensitive or PII.
Those same models can be stored back in your database so they can be accessed via SQL.
Once you've marked up all of your sensitive attributes/columns, and store it back into the database, you can query it back out.
Disclaimer: I work for Oracle, I'm the product manager for Data Modeler.
[TL;DR] Don't do it. Find another way.
If it's advisable
NO
Never modify the data dictionary; (unless Oracle support tells you to) you are likely to invalidate your support contract with Oracle and may break the database and make it unusable.
If it's possible
Don't do this.
If you really want to try it then still don't.
If you really, really want to try it then find a database you don't care about (the don't care about bit is important!) and log on as a SYSDBA user and:
ALTER TABLE whichever_data_dictionary_table ADD anonymisation_flag VARCHAR2(10);
Then you can test whether the database breaks (and it may not break immediately but at some point later), but if it does then you almost certainly will not get any support from Oracle in fixing it.
Did we say, "Don't do it"... we mean it.
As you already know, you shouldn't do that.
But, nothing prevents you from creating your own table which will contain such an info.
For example:
SQL> CREATE TABLE my_comments
2 (
3 table_name VARCHAR2 (30),
4 column_name VARCHAR2 (30),
5 anonymisation VARCHAR2 (10)
6 );
Table created.
Populate it with some data:
SQL> insert into my_comments (table_name, column_name)
2 select table_name, column_name
3 from user_tab_columns
4 where table_name = 'DEPT';
3 rows created.
Set the anonymisation flag:
SQL> update my_comments set anonymisation = 'F' where column_name = 'DEPTNO';
1 row updated.
When you want to get such an info (along with some more data from user_tab_columns, use (outer) join:
SQL> select u.table_name, u.column_name, u.data_type, u.nullable, m.anonymisation
2 from user_tab_columns u left join my_comments m on m.table_name = u.table_name
3 and m.column_name = u.column_name
4 where u.column_name = 'DEPTNO';
TABLE_NAME COLUMN_NAME DATA_TYPE N ANONYMISATION
---------- --------------- ------------ - ---------------
DEPT DEPTNO NUMBER N F
DSV DEPTNO NUMBER N
DSMV DEPTNO NUMBER Y
EMP DEPTNO NUMBER Y
SQL>
Advantages: you won't break the database & you'll have your additional info.
Drawbacks: you'll have to maintain the table manually.
I would like to know if it exists an Oracle command to know if a DB-LINK (name: myBDLink) is used somewhere in a DB and how to display the objects (views,materialized views, procedures, functions, ...) which use it.
Could you please help me with that ?
Thanks for your help
Well, you could try to query various system views and see whether any of them contains a string you're looking for. As you want to check the whole database, you'll probably connect as a privileged user and check dba_ views; otherwise, all_ or user_ would do.
For example, to check procedures, functions, packages, ...:
select owner, name, type, line
from dba_source
where owner not in ('SYS', 'SYSTEM')
and lower(text) like '%mydblink%';
To check views, you'll need a function which will search through its LONG datatype column (as you can't use it directly in SQL):
create or replace function f_long(par_view in varchar2, par_String in varchar2)
return varchar2
is
l_text varchar2(32000);
begin
select text
into l_text
from dba_views
where owner not in ('SYS', 'SYSTEM')
and view_name = par_view;
return case when instr(lower(l_text), lower(par_string)) > 0 then 1
else 0
end;
end;
/
and then
select owner, view_name
from dba_views
where f_long(view_name, 'mydblink') = 1;
I excluded SYS and SYSTEM as they should not contain anything of users' stuff. Perhaps you'd want to exclude some more users.
To see some more (re)sources, query the dictionary, e.g.
select table_name, comments
from dictionary;
TABLE_NAME COMMENTS
------------------------------ --------------------------------------------------
USER_CONS_COLUMNS Information about accessible columns in constraint
definitions
ALL_CONS_COLUMNS Information about accessible columns in constraint
definitions
DBA_CONS_COLUMNS Information about accessible columns in constraint
definitions
<snip>
There is no complete answer. How would the database know of code that is outside of the database? It can't. So if you have a sql script, or some application that does not rely on stored procedures to do everything, the database will not know of them.
That said, for dependencies that are in stored procedures in the database, you can try this:
select *
from dba_dependencies
where referenced_link_name is not null
;
To add to the other (correct) answers that have been posted by #Littlefoot and #EdStevens, a quick-and-dirty analysis can also be made against the Automated Workload Repository (AWR).
The benefit of this approach is it will find usages of remote objects from SQL submitted to the database whether that SQL is in DBA_SOURCE or not (e.g., is embedded in an external application).
-- Find any objects referenced across a database link (sort of)
select object_node, object_name, count(distinct sql_id) sql_id_count
from dba_hist_sql_plan
where object_type = 'REMOTE'
group by object_node, object_name
order by object_node, object_name
;
The problem is that AWR data isn't 100% complete. First of all, it's not kept around forever, so a database link last used more than a month (or two months or however long your DBAs keep AWR data for) wouldn't be seen. Second of all, AWR only takes snapshots periodically, say every hour. So it's theoretically possible for a SQL to use a database link and then get aged out of the library cache before the next AWR snapshot.
I think the chance of missing something due to that last bit is small on the systems I work with. But, if you have poorly written applications (i.e., no bind variables) and limited shared pool space, it's something to worry about.
Since I am new to Oracle, please tell me what different ways to find packages, stored procedures, triggers, functions, indexes, tablespaces
Thanks
The following statement gives you an overview of all database objects in the current user:
SELECT
object_name,
object_type
FROM
user_objects;
If you are searching for documentation, you can look at Morgan's Library
You can download Oracle SQL Developer free. This allows you to explore all the objects in your database via a simple interface.
I shall walk you through the different shades of "all_object":
SQL> show user
USER is "C##SCOTT"
SQL>
Getting all the types of object:
select distinct object_type from all_objects;
EDITION
CONSUMER GROUP
SEQUENCE
SCHEDULE
PROCEDURE
OPERATOR
DESTINATION
WINDOW
SCHEDULER GROUP
PACKAGE
PROGRAM
LOB
XML SCHEMA
JAVA RESOURCE
JOB CLASS
DIRECTORY
TABLE
SYNONYM
INDEX
VIEW
FUNCTION
INDEXTYPE
JAVA CLASS
TYPE
EVALUATION CONTEXT
25 rows selected.
Now, you can zoom down to the "TABLE" type of object:
select object_name||','||object_id||','||owner from all_objects where object_type='TABLE' ;
Or all the objects of an owner:
select object_name||','||object_id||','||OBJECT_TYPE from all_objects where owner = 'SYS';
Trust me, you will learn more this way - anyone can click through any GUI tool, but to issue the SQL command, you will need some knowledge.
I've heard people referring to this table and was not sure what it was about.
It's a sort of dummy table with a single record used for selecting when you're not actually interested in the data, but instead want the results of some system function in a select statement:
e.g. select sysdate from dual;
See http://www.adp-gmbh.ch/ora/misc/dual.html
As of 23c, Oracle supports select sysdate /* or other value */, without from dual, as has been supported in MySQL for some time already.
It is a dummy table with one element in it. It is useful because Oracle doesn't allow statements like
SELECT 3+4
You can work around this restriction by writing
SELECT 3+4 FROM DUAL
instead.
From Wikipedia
History
The DUAL table was created by Chuck Weiss of Oracle corporation to provide a table for joining in internal views:
I created the DUAL table as an underlying object in the Oracle Data Dictionary. It was never meant to be seen itself, but instead used
inside a view that was expected to be queried. The idea was that you
could do a JOIN to the DUAL table and create two rows in the result
for every one row in your table. Then, by using GROUP BY, the
resulting join could be summarized to show the amount of storage for
the DATA extent and for the INDEX extent(s). The name, DUAL, seemed
apt for the process of creating a pair of rows from just one. 1
It may not be obvious from the above, but the original DUAL table had two rows in it (hence its name). Nowadays it only has one row.
Optimization
DUAL was originally a table and the database engine would perform disk IO on the table when selecting from DUAL. This disk IO was usually logical IO (not involving physical disk access) as the disk blocks were usually already cached in memory. This resulted in a large amount of logical IO against the DUAL table.
Later versions of the Oracle database have been optimized and the database no longer performs physical or logical IO on the DUAL table even though the DUAL table still actually exists.
I think this wikipedia article may help clarify.
http://en.wikipedia.org/wiki/DUAL_table
The DUAL table is a special one-row
table present by default in all Oracle
database installations. It is suitable
for use in selecting a pseudocolumn
such as SYSDATE or USER The table has
a single VARCHAR2(1) column called
DUMMY that has a value of "X"
It's the special table in Oracle. I often use it for calculations or checking system variables. For example:
Select 2*4 from dual prints out the result of the calculation
Select sysdate from dual prints the server current date.
A utility table in Oracle with only 1 row and 1 column. It is used to perform a number of arithmetic operations and can be used generally where one needs to generate a known output.
SELECT * FROM dual;
will give a single row, with a single column named "DUMMY" and a value of "X" as shown here:
DUMMY
-----
X
Kind of a pseudo table you can run commands against and get back results, such as sysdate. Also helps you to check if Oracle is up and check sql syntax, etc.
The DUAL table is a special one-row table present by default in all Oracle database installations. It is suitable for use in selecting a pseudocolumn such as SYSDATE or USER
The table has a single VARCHAR2(1) column called DUMMY that has a value of "X"
You can read all about it in http://en.wikipedia.org/wiki/DUAL_table
DUAL is necessary in PL/SQL development for using functions that are only available in SQL
e.g.
DECLARE
x XMLTYPE;
BEGIN
SELECT xmlelement("hhh", 'stuff')
INTO x
FROM dual;
END;
More Facts about the DUAL....
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1562813956388
Thrilling experiments done here, and more thrilling explanations by Tom
DUAL we mainly used for getting the next number from the sequences.
Syntax : SELECT 'sequence_name'.NEXTVAL FROM DUAL
This will return the one row one column value(NEXTVAL column name).
another situation which requires select ... from dual is when we want to retrieve the code (data definition) for different database objects (like TABLE, FUNCTION, TRIGGER, PACKAGE), using the built in DBMS_METADATA.GET_DDL function:
select DBMS_METADATA.GET_DDL('TABLE','<table_name>') from DUAL;
select DBMS_METADATA.GET_DDL('FUNCTION','<function_name>') from DUAL;
in is true that nowadays the IDEs do offer the capability to view the DDL of a table, but in simpler environments like SQL Plus this can be really handy.
EDIT
a more general situation: basically, when we need to use any PL/SQL procedure inside a standard SQL statement, or when we want to call a procedure from the command line:
select my_function(<input_params>) from dual;
both recipes are taken from the book 'Oracle PL/SQL Recipes' by Josh Juneau and Matt Arena
The DUAL is special one row, one column table present by default in all Oracle databases. The owner of DUAL is SYS.
DUAL is a table automatically created by Oracle Database along with the data functions. It is always used to get the operating systems functions(like date, time, arithmetic expression., etc.)
SELECT SYSDATE from dual;
It's a object to put in the from that return 1 empty row. For example:
select 1 from dual;
returns 1
select 21+44 from dual;
returns 65
select [sequence].nextval from dual;
returns the next value from the sequence.