My Ramblings with Oracle-11g

Intro :

I have recently started using Oracle 11g and boy, doesn’t it come with enough problems already!! However, it may be due to my undying allegiance to mysql and sqlite. But whatever be the case.

Here are some of the things which I found would be useful to a first time user of Oracle 11g. I will try to update it when I find something useful.

If you haven’t already installed Oracle 11g. I wrote a small article on how to do so sometime back.

Creating a new user :

Now we can use the default users SYSTEM or SYS, but I prefer creating my own here.

To do that

tasdik@Acer:~$ sqlplus

SQL*Plus: Release 11.2.0.2.0 Production on Sat Sep 26 14:25:09 2015

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Enter user-name: SYSTEM
Enter password: 

Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

SQL> create user lab identified by lab;

User created.

## check the new user 

SQL> select username from dba_users ;

USERNAME
------------------------------
LAB
SYS
SYSTEM
ANONYMOUS
APEX_PUBLIC_USER
APEX_040000
OUTLN
XS$NULL
FLOWS_FILES
MDSYS

USERNAME
------------------------------
CTXSYS
XDB
HR

14 rows selected.

SQL> grant create session to lab ;

Grant succeeded.

SQL> grant connect to lab ;

Grant succeeded.

SQL> grant all privileges to lab ; 

Grant succeeded.

SQL> exit
Disconnected from Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

Now connect to the new user lab

tasdik@Acer:~$ sqlplus

SQL*Plus: Release 11.2.0.2.0 Production on Sat Sep 26 14:34:10 2015

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Enter user-name: lab
Enter password: 

Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production


## clear the screen
SQL> cl scr

SQL> select table_name from user_tables ;

no rows selected
## as no tables have been created by the user `lab` till now
## so lets create some, shall we

SQL> CREATE TABLE department (
  2   dept_name varchar(20), 
  3   building varchar(15), 
  4   budget numeric(12,2) check (budget > 0), 
  5   primary key (dept_name)
  6  ) ; 

Table created.

SQL> select table_name from user_tables ; 

TABLE_NAME
------------------------------
DEPARTMENT

## you can do whatever you can normally do with this user
SQL> drop table department ; 

Table dropped.

SQL> select table_name from user_tables ;

no rows selected

SQL> 

To Delete a User :

After dropping the user, you need to, for each related tablespace, take it offline and drop it. For example if you had a user named ‘SAMPLE’ and two tablespaces called ‘SAMPLE’ and ‘SAMPLE_INDEX’, then you’d need to do the following:

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DROP USER SAMPLE CASCADE;
ALTER TABLESPACE SAMPLE OFFLINE;
DROP TABLESPACE SAMPLE INCLUDING CONTENTS;
ALTER TABLESPACE SAMPLE_INDEX OFFLINE;
DROP TABLESPACE SAMPLE_INDEX INCLUDING CONTENTS;

There is no such thing as IF EXISTS :

I mean what! I find this really irritating in the part of Oracle to not give support for this feature as any other major RDMS system implements this.

Lets try it out

SQL> select table_name from user_tables ; 

no rows selected

SQL>

So we don’t have any relations right now. Lets try to drop tasdik which does not exist the way we do in mysql.

SQL> DROP TABLE IF EXISTS tasdik ; 
DROP TABLE IF EXISTS tasdik
              *
ERROR at line 1:
ORA-00933: SQL command not properly ended


SQL>

If you try to DROP a relation which does not exist, the query will not stop executing in the middle, but will just give you an error like the above

Well, sqlite has a limitation where we cannot alter the attribute in a relation, like add or delete an attribute to a relation. So nobody is perfect here.

No support for cursor keys :

[email protected]:~$ sqlplus

SQL*Plus: Release 11.2.0.2.0 Production on Sun Sep 27 19:12:41 2015

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Enter user-name: lab
Enter password: 

Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

SQL> ^[[A^[[A^[[A

As you can see, whenever you press the cursor keys, there is garbage on the screen. Now I was not sure why this was happening. Turns out it doesn’t support the arrow keys in *nix based systems. (Good news for those on windows).

But well there is a workaround.

You can use a third party utility called rlwrap.

rlwrap is a readline wrapper, a small utility that uses the GNU readline library to allow the editing of keyboard input for any other command. It maintains a separate input history for each command, and can TAB-expand words using all previously seen words and/or a user-specified file.So you will be able to use arrows and also get a command history as a bonus.

After you have installed the utility run sqlplus the following way:

[email protected]:~$ rlwrap sqlplus

SQL*Plus: Release 11.2.0.2.0 Production on Sun Sep 27 19:04:38 2015

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Enter user-name: lab
Enter password: 

Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

SQL>

And the arrow keys would work just fine

References:

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